This is libc.info, produced by makeinfo version 5.1 from libc.texinfo.

This file documents the GNU C Library.

   This is ‘The GNU C Library Reference Manual’, for version 2.30.

   Copyright © 1993–2019 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being “Free Software Needs Free Documentation” and
“GNU Lesser General Public License”, the Front-Cover texts being “A GNU
Manual”, and with the Back-Cover Texts as in (a) below.  A copy of the
license is included in the section entitled "GNU Free Documentation
License".

   (a) The FSF’s Back-Cover Text is: “You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom.”
INFO-DIR-SECTION Software libraries
START-INFO-DIR-ENTRY
* Libc: (libc).                 C library.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION GNU C library functions and macros
START-INFO-DIR-ENTRY
* ALTWERASE: (libc)Local Modes.
* ARGP_ERR_UNKNOWN: (libc)Argp Parser Functions.
* ARG_MAX: (libc)General Limits.
* BC_BASE_MAX: (libc)Utility Limits.
* BC_DIM_MAX: (libc)Utility Limits.
* BC_SCALE_MAX: (libc)Utility Limits.
* BC_STRING_MAX: (libc)Utility Limits.
* BRKINT: (libc)Input Modes.
* BUFSIZ: (libc)Controlling Buffering.
* CCTS_OFLOW: (libc)Control Modes.
* CHAR_BIT: (libc)Width of Type.
* CHILD_MAX: (libc)General Limits.
* CIGNORE: (libc)Control Modes.
* CLK_TCK: (libc)Processor Time.
* CLOCAL: (libc)Control Modes.
* CLOCKS_PER_SEC: (libc)CPU Time.
* COLL_WEIGHTS_MAX: (libc)Utility Limits.
* CPU_CLR: (libc)CPU Affinity.
* CPU_ISSET: (libc)CPU Affinity.
* CPU_SET: (libc)CPU Affinity.
* CPU_SETSIZE: (libc)CPU Affinity.
* CPU_ZERO: (libc)CPU Affinity.
* CREAD: (libc)Control Modes.
* CRTS_IFLOW: (libc)Control Modes.
* CS5: (libc)Control Modes.
* CS6: (libc)Control Modes.
* CS7: (libc)Control Modes.
* CS8: (libc)Control Modes.
* CSIZE: (libc)Control Modes.
* CSTOPB: (libc)Control Modes.
* DTTOIF: (libc)Directory Entries.
* E2BIG: (libc)Error Codes.
* EACCES: (libc)Error Codes.
* EADDRINUSE: (libc)Error Codes.
* EADDRNOTAVAIL: (libc)Error Codes.
* EADV: (libc)Error Codes.
* EAFNOSUPPORT: (libc)Error Codes.
* EAGAIN: (libc)Error Codes.
* EALREADY: (libc)Error Codes.
* EAUTH: (libc)Error Codes.
* EBACKGROUND: (libc)Error Codes.
* EBADE: (libc)Error Codes.
* EBADF: (libc)Error Codes.
* EBADFD: (libc)Error Codes.
* EBADMSG: (libc)Error Codes.
* EBADR: (libc)Error Codes.
* EBADRPC: (libc)Error Codes.
* EBADRQC: (libc)Error Codes.
* EBADSLT: (libc)Error Codes.
* EBFONT: (libc)Error Codes.
* EBUSY: (libc)Error Codes.
* ECANCELED: (libc)Error Codes.
* ECHILD: (libc)Error Codes.
* ECHO: (libc)Local Modes.
* ECHOCTL: (libc)Local Modes.
* ECHOE: (libc)Local Modes.
* ECHOK: (libc)Local Modes.
* ECHOKE: (libc)Local Modes.
* ECHONL: (libc)Local Modes.
* ECHOPRT: (libc)Local Modes.
* ECHRNG: (libc)Error Codes.
* ECOMM: (libc)Error Codes.
* ECONNABORTED: (libc)Error Codes.
* ECONNREFUSED: (libc)Error Codes.
* ECONNRESET: (libc)Error Codes.
* ED: (libc)Error Codes.
* EDEADLK: (libc)Error Codes.
* EDEADLOCK: (libc)Error Codes.
* EDESTADDRREQ: (libc)Error Codes.
* EDIED: (libc)Error Codes.
* EDOM: (libc)Error Codes.
* EDOTDOT: (libc)Error Codes.
* EDQUOT: (libc)Error Codes.
* EEXIST: (libc)Error Codes.
* EFAULT: (libc)Error Codes.
* EFBIG: (libc)Error Codes.
* EFTYPE: (libc)Error Codes.
* EGRATUITOUS: (libc)Error Codes.
* EGREGIOUS: (libc)Error Codes.
* EHOSTDOWN: (libc)Error Codes.
* EHOSTUNREACH: (libc)Error Codes.
* EHWPOISON: (libc)Error Codes.
* EIDRM: (libc)Error Codes.
* EIEIO: (libc)Error Codes.
* EILSEQ: (libc)Error Codes.
* EINPROGRESS: (libc)Error Codes.
* EINTR: (libc)Error Codes.
* EINVAL: (libc)Error Codes.
* EIO: (libc)Error Codes.
* EISCONN: (libc)Error Codes.
* EISDIR: (libc)Error Codes.
* EISNAM: (libc)Error Codes.
* EKEYEXPIRED: (libc)Error Codes.
* EKEYREJECTED: (libc)Error Codes.
* EKEYREVOKED: (libc)Error Codes.
* EL2HLT: (libc)Error Codes.
* EL2NSYNC: (libc)Error Codes.
* EL3HLT: (libc)Error Codes.
* EL3RST: (libc)Error Codes.
* ELIBACC: (libc)Error Codes.
* ELIBBAD: (libc)Error Codes.
* ELIBEXEC: (libc)Error Codes.
* ELIBMAX: (libc)Error Codes.
* ELIBSCN: (libc)Error Codes.
* ELNRNG: (libc)Error Codes.
* ELOOP: (libc)Error Codes.
* EMEDIUMTYPE: (libc)Error Codes.
* EMFILE: (libc)Error Codes.
* EMLINK: (libc)Error Codes.
* EMSGSIZE: (libc)Error Codes.
* EMULTIHOP: (libc)Error Codes.
* ENAMETOOLONG: (libc)Error Codes.
* ENAVAIL: (libc)Error Codes.
* ENEEDAUTH: (libc)Error Codes.
* ENETDOWN: (libc)Error Codes.
* ENETRESET: (libc)Error Codes.
* ENETUNREACH: (libc)Error Codes.
* ENFILE: (libc)Error Codes.
* ENOANO: (libc)Error Codes.
* ENOBUFS: (libc)Error Codes.
* ENOCSI: (libc)Error Codes.
* ENODATA: (libc)Error Codes.
* ENODEV: (libc)Error Codes.
* ENOENT: (libc)Error Codes.
* ENOEXEC: (libc)Error Codes.
* ENOKEY: (libc)Error Codes.
* ENOLCK: (libc)Error Codes.
* ENOLINK: (libc)Error Codes.
* ENOMEDIUM: (libc)Error Codes.
* ENOMEM: (libc)Error Codes.
* ENOMSG: (libc)Error Codes.
* ENONET: (libc)Error Codes.
* ENOPKG: (libc)Error Codes.
* ENOPROTOOPT: (libc)Error Codes.
* ENOSPC: (libc)Error Codes.
* ENOSR: (libc)Error Codes.
* ENOSTR: (libc)Error Codes.
* ENOSYS: (libc)Error Codes.
* ENOTBLK: (libc)Error Codes.
* ENOTCONN: (libc)Error Codes.
* ENOTDIR: (libc)Error Codes.
* ENOTEMPTY: (libc)Error Codes.
* ENOTNAM: (libc)Error Codes.
* ENOTRECOVERABLE: (libc)Error Codes.
* ENOTSOCK: (libc)Error Codes.
* ENOTSUP: (libc)Error Codes.
* ENOTTY: (libc)Error Codes.
* ENOTUNIQ: (libc)Error Codes.
* ENXIO: (libc)Error Codes.
* EOF: (libc)EOF and Errors.
* EOPNOTSUPP: (libc)Error Codes.
* EOVERFLOW: (libc)Error Codes.
* EOWNERDEAD: (libc)Error Codes.
* EPERM: (libc)Error Codes.
* EPFNOSUPPORT: (libc)Error Codes.
* EPIPE: (libc)Error Codes.
* EPROCLIM: (libc)Error Codes.
* EPROCUNAVAIL: (libc)Error Codes.
* EPROGMISMATCH: (libc)Error Codes.
* EPROGUNAVAIL: (libc)Error Codes.
* EPROTO: (libc)Error Codes.
* EPROTONOSUPPORT: (libc)Error Codes.
* EPROTOTYPE: (libc)Error Codes.
* EQUIV_CLASS_MAX: (libc)Utility Limits.
* ERANGE: (libc)Error Codes.
* EREMCHG: (libc)Error Codes.
* EREMOTE: (libc)Error Codes.
* EREMOTEIO: (libc)Error Codes.
* ERESTART: (libc)Error Codes.
* ERFKILL: (libc)Error Codes.
* EROFS: (libc)Error Codes.
* ERPCMISMATCH: (libc)Error Codes.
* ESHUTDOWN: (libc)Error Codes.
* ESOCKTNOSUPPORT: (libc)Error Codes.
* ESPIPE: (libc)Error Codes.
* ESRCH: (libc)Error Codes.
* ESRMNT: (libc)Error Codes.
* ESTALE: (libc)Error Codes.
* ESTRPIPE: (libc)Error Codes.
* ETIME: (libc)Error Codes.
* ETIMEDOUT: (libc)Error Codes.
* ETOOMANYREFS: (libc)Error Codes.
* ETXTBSY: (libc)Error Codes.
* EUCLEAN: (libc)Error Codes.
* EUNATCH: (libc)Error Codes.
* EUSERS: (libc)Error Codes.
* EWOULDBLOCK: (libc)Error Codes.
* EXDEV: (libc)Error Codes.
* EXFULL: (libc)Error Codes.
* EXIT_FAILURE: (libc)Exit Status.
* EXIT_SUCCESS: (libc)Exit Status.
* EXPR_NEST_MAX: (libc)Utility Limits.
* FD_CLOEXEC: (libc)Descriptor Flags.
* FD_CLR: (libc)Waiting for I/O.
* FD_ISSET: (libc)Waiting for I/O.
* FD_SET: (libc)Waiting for I/O.
* FD_SETSIZE: (libc)Waiting for I/O.
* FD_ZERO: (libc)Waiting for I/O.
* FE_SNANS_ALWAYS_SIGNAL: (libc)Infinity and NaN.
* FILENAME_MAX: (libc)Limits for Files.
* FLUSHO: (libc)Local Modes.
* FOPEN_MAX: (libc)Opening Streams.
* FP_ILOGB0: (libc)Exponents and Logarithms.
* FP_ILOGBNAN: (libc)Exponents and Logarithms.
* FP_LLOGB0: (libc)Exponents and Logarithms.
* FP_LLOGBNAN: (libc)Exponents and Logarithms.
* F_DUPFD: (libc)Duplicating Descriptors.
* F_GETFD: (libc)Descriptor Flags.
* F_GETFL: (libc)Getting File Status Flags.
* F_GETLK: (libc)File Locks.
* F_GETOWN: (libc)Interrupt Input.
* F_OFD_GETLK: (libc)Open File Description Locks.
* F_OFD_SETLK: (libc)Open File Description Locks.
* F_OFD_SETLKW: (libc)Open File Description Locks.
* F_OK: (libc)Testing File Access.
* F_SETFD: (libc)Descriptor Flags.
* F_SETFL: (libc)Getting File Status Flags.
* F_SETLK: (libc)File Locks.
* F_SETLKW: (libc)File Locks.
* F_SETOWN: (libc)Interrupt Input.
* HUGE_VAL: (libc)Math Error Reporting.
* HUGE_VALF: (libc)Math Error Reporting.
* HUGE_VALL: (libc)Math Error Reporting.
* HUGE_VAL_FN: (libc)Math Error Reporting.
* HUGE_VAL_FNx: (libc)Math Error Reporting.
* HUPCL: (libc)Control Modes.
* I: (libc)Complex Numbers.
* ICANON: (libc)Local Modes.
* ICRNL: (libc)Input Modes.
* IEXTEN: (libc)Local Modes.
* IFNAMSIZ: (libc)Interface Naming.
* IFTODT: (libc)Directory Entries.
* IGNBRK: (libc)Input Modes.
* IGNCR: (libc)Input Modes.
* IGNPAR: (libc)Input Modes.
* IMAXBEL: (libc)Input Modes.
* INADDR_ANY: (libc)Host Address Data Type.
* INADDR_BROADCAST: (libc)Host Address Data Type.
* INADDR_LOOPBACK: (libc)Host Address Data Type.
* INADDR_NONE: (libc)Host Address Data Type.
* INFINITY: (libc)Infinity and NaN.
* INLCR: (libc)Input Modes.
* INPCK: (libc)Input Modes.
* IPPORT_RESERVED: (libc)Ports.
* IPPORT_USERRESERVED: (libc)Ports.
* ISIG: (libc)Local Modes.
* ISTRIP: (libc)Input Modes.
* IXANY: (libc)Input Modes.
* IXOFF: (libc)Input Modes.
* IXON: (libc)Input Modes.
* LINE_MAX: (libc)Utility Limits.
* LINK_MAX: (libc)Limits for Files.
* L_ctermid: (libc)Identifying the Terminal.
* L_cuserid: (libc)Who Logged In.
* L_tmpnam: (libc)Temporary Files.
* MAXNAMLEN: (libc)Limits for Files.
* MAXSYMLINKS: (libc)Symbolic Links.
* MAX_CANON: (libc)Limits for Files.
* MAX_INPUT: (libc)Limits for Files.
* MB_CUR_MAX: (libc)Selecting the Conversion.
* MB_LEN_MAX: (libc)Selecting the Conversion.
* MDMBUF: (libc)Control Modes.
* MSG_DONTROUTE: (libc)Socket Data Options.
* MSG_OOB: (libc)Socket Data Options.
* MSG_PEEK: (libc)Socket Data Options.
* NAME_MAX: (libc)Limits for Files.
* NAN: (libc)Infinity and NaN.
* NCCS: (libc)Mode Data Types.
* NGROUPS_MAX: (libc)General Limits.
* NOFLSH: (libc)Local Modes.
* NOKERNINFO: (libc)Local Modes.
* NSIG: (libc)Standard Signals.
* NULL: (libc)Null Pointer Constant.
* ONLCR: (libc)Output Modes.
* ONOEOT: (libc)Output Modes.
* OPEN_MAX: (libc)General Limits.
* OPOST: (libc)Output Modes.
* OXTABS: (libc)Output Modes.
* O_ACCMODE: (libc)Access Modes.
* O_APPEND: (libc)Operating Modes.
* O_ASYNC: (libc)Operating Modes.
* O_CREAT: (libc)Open-time Flags.
* O_DIRECTORY: (libc)Open-time Flags.
* O_EXCL: (libc)Open-time Flags.
* O_EXEC: (libc)Access Modes.
* O_EXLOCK: (libc)Open-time Flags.
* O_FSYNC: (libc)Operating Modes.
* O_IGNORE_CTTY: (libc)Open-time Flags.
* O_NDELAY: (libc)Operating Modes.
* O_NOATIME: (libc)Operating Modes.
* O_NOCTTY: (libc)Open-time Flags.
* O_NOLINK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Operating Modes.
* O_NOTRANS: (libc)Open-time Flags.
* O_RDONLY: (libc)Access Modes.
* O_RDWR: (libc)Access Modes.
* O_READ: (libc)Access Modes.
* O_SHLOCK: (libc)Open-time Flags.
* O_SYNC: (libc)Operating Modes.
* O_TMPFILE: (libc)Open-time Flags.
* O_TRUNC: (libc)Open-time Flags.
* O_WRITE: (libc)Access Modes.
* O_WRONLY: (libc)Access Modes.
* PARENB: (libc)Control Modes.
* PARMRK: (libc)Input Modes.
* PARODD: (libc)Control Modes.
* PATH_MAX: (libc)Limits for Files.
* PA_FLAG_MASK: (libc)Parsing a Template String.
* PENDIN: (libc)Local Modes.
* PF_FILE: (libc)Local Namespace Details.
* PF_INET6: (libc)Internet Namespace.
* PF_INET: (libc)Internet Namespace.
* PF_LOCAL: (libc)Local Namespace Details.
* PF_UNIX: (libc)Local Namespace Details.
* PIPE_BUF: (libc)Limits for Files.
* P_tmpdir: (libc)Temporary Files.
* RAND_MAX: (libc)ISO Random.
* RE_DUP_MAX: (libc)General Limits.
* RLIM_INFINITY: (libc)Limits on Resources.
* R_OK: (libc)Testing File Access.
* SA_NOCLDSTOP: (libc)Flags for Sigaction.
* SA_ONSTACK: (libc)Flags for Sigaction.
* SA_RESTART: (libc)Flags for Sigaction.
* SEEK_CUR: (libc)File Positioning.
* SEEK_END: (libc)File Positioning.
* SEEK_SET: (libc)File Positioning.
* SIGABRT: (libc)Program Error Signals.
* SIGALRM: (libc)Alarm Signals.
* SIGBUS: (libc)Program Error Signals.
* SIGCHLD: (libc)Job Control Signals.
* SIGCLD: (libc)Job Control Signals.
* SIGCONT: (libc)Job Control Signals.
* SIGEMT: (libc)Program Error Signals.
* SIGFPE: (libc)Program Error Signals.
* SIGHUP: (libc)Termination Signals.
* SIGILL: (libc)Program Error Signals.
* SIGINFO: (libc)Miscellaneous Signals.
* SIGINT: (libc)Termination Signals.
* SIGIO: (libc)Asynchronous I/O Signals.
* SIGIOT: (libc)Program Error Signals.
* SIGKILL: (libc)Termination Signals.
* SIGLOST: (libc)Operation Error Signals.
* SIGPIPE: (libc)Operation Error Signals.
* SIGPOLL: (libc)Asynchronous I/O Signals.
* SIGPROF: (libc)Alarm Signals.
* SIGQUIT: (libc)Termination Signals.
* SIGSEGV: (libc)Program Error Signals.
* SIGSTOP: (libc)Job Control Signals.
* SIGSYS: (libc)Program Error Signals.
* SIGTERM: (libc)Termination Signals.
* SIGTRAP: (libc)Program Error Signals.
* SIGTSTP: (libc)Job Control Signals.
* SIGTTIN: (libc)Job Control Signals.
* SIGTTOU: (libc)Job Control Signals.
* SIGURG: (libc)Asynchronous I/O Signals.
* SIGUSR1: (libc)Miscellaneous Signals.
* SIGUSR2: (libc)Miscellaneous Signals.
* SIGVTALRM: (libc)Alarm Signals.
* SIGWINCH: (libc)Miscellaneous Signals.
* SIGXCPU: (libc)Operation Error Signals.
* SIGXFSZ: (libc)Operation Error Signals.
* SIG_ERR: (libc)Basic Signal Handling.
* SNAN: (libc)Infinity and NaN.
* SNANF: (libc)Infinity and NaN.
* SNANFN: (libc)Infinity and NaN.
* SNANFNx: (libc)Infinity and NaN.
* SNANL: (libc)Infinity and NaN.
* SOCK_DGRAM: (libc)Communication Styles.
* SOCK_RAW: (libc)Communication Styles.
* SOCK_RDM: (libc)Communication Styles.
* SOCK_SEQPACKET: (libc)Communication Styles.
* SOCK_STREAM: (libc)Communication Styles.
* SOL_SOCKET: (libc)Socket-Level Options.
* SSIZE_MAX: (libc)General Limits.
* STREAM_MAX: (libc)General Limits.
* SUN_LEN: (libc)Local Namespace Details.
* S_IFMT: (libc)Testing File Type.
* S_ISBLK: (libc)Testing File Type.
* S_ISCHR: (libc)Testing File Type.
* S_ISDIR: (libc)Testing File Type.
* S_ISFIFO: (libc)Testing File Type.
* S_ISLNK: (libc)Testing File Type.
* S_ISREG: (libc)Testing File Type.
* S_ISSOCK: (libc)Testing File Type.
* S_TYPEISMQ: (libc)Testing File Type.
* S_TYPEISSEM: (libc)Testing File Type.
* S_TYPEISSHM: (libc)Testing File Type.
* TMP_MAX: (libc)Temporary Files.
* TOSTOP: (libc)Local Modes.
* TZNAME_MAX: (libc)General Limits.
* VDISCARD: (libc)Other Special.
* VDSUSP: (libc)Signal Characters.
* VEOF: (libc)Editing Characters.
* VEOL2: (libc)Editing Characters.
* VEOL: (libc)Editing Characters.
* VERASE: (libc)Editing Characters.
* VINTR: (libc)Signal Characters.
* VKILL: (libc)Editing Characters.
* VLNEXT: (libc)Other Special.
* VMIN: (libc)Noncanonical Input.
* VQUIT: (libc)Signal Characters.
* VREPRINT: (libc)Editing Characters.
* VSTART: (libc)Start/Stop Characters.
* VSTATUS: (libc)Other Special.
* VSTOP: (libc)Start/Stop Characters.
* VSUSP: (libc)Signal Characters.
* VTIME: (libc)Noncanonical Input.
* VWERASE: (libc)Editing Characters.
* WCHAR_MAX: (libc)Extended Char Intro.
* WCHAR_MIN: (libc)Extended Char Intro.
* WCOREDUMP: (libc)Process Completion Status.
* WEOF: (libc)EOF and Errors.
* WEOF: (libc)Extended Char Intro.
* WEXITSTATUS: (libc)Process Completion Status.
* WIFEXITED: (libc)Process Completion Status.
* WIFSIGNALED: (libc)Process Completion Status.
* WIFSTOPPED: (libc)Process Completion Status.
* WSTOPSIG: (libc)Process Completion Status.
* WTERMSIG: (libc)Process Completion Status.
* W_OK: (libc)Testing File Access.
* X_OK: (libc)Testing File Access.
* _Complex_I: (libc)Complex Numbers.
* _Exit: (libc)Termination Internals.
* _IOFBF: (libc)Controlling Buffering.
* _IOLBF: (libc)Controlling Buffering.
* _IONBF: (libc)Controlling Buffering.
* _Imaginary_I: (libc)Complex Numbers.
* _PATH_UTMP: (libc)Manipulating the Database.
* _PATH_WTMP: (libc)Manipulating the Database.
* _POSIX2_C_DEV: (libc)System Options.
* _POSIX2_C_VERSION: (libc)Version Supported.
* _POSIX2_FORT_DEV: (libc)System Options.
* _POSIX2_FORT_RUN: (libc)System Options.
* _POSIX2_LOCALEDEF: (libc)System Options.
* _POSIX2_SW_DEV: (libc)System Options.
* _POSIX_CHOWN_RESTRICTED: (libc)Options for Files.
* _POSIX_JOB_CONTROL: (libc)System Options.
* _POSIX_NO_TRUNC: (libc)Options for Files.
* _POSIX_SAVED_IDS: (libc)System Options.
* _POSIX_VDISABLE: (libc)Options for Files.
* _POSIX_VERSION: (libc)Version Supported.
* __fbufsize: (libc)Controlling Buffering.
* __flbf: (libc)Controlling Buffering.
* __fpending: (libc)Controlling Buffering.
* __fpurge: (libc)Flushing Buffers.
* __freadable: (libc)Opening Streams.
* __freading: (libc)Opening Streams.
* __fsetlocking: (libc)Streams and Threads.
* __fwritable: (libc)Opening Streams.
* __fwriting: (libc)Opening Streams.
* __gconv_end_fct: (libc)glibc iconv Implementation.
* __gconv_fct: (libc)glibc iconv Implementation.
* __gconv_init_fct: (libc)glibc iconv Implementation.
* __ppc_get_timebase: (libc)PowerPC.
* __ppc_get_timebase_freq: (libc)PowerPC.
* __ppc_mdoio: (libc)PowerPC.
* __ppc_mdoom: (libc)PowerPC.
* __ppc_set_ppr_low: (libc)PowerPC.
* __ppc_set_ppr_med: (libc)PowerPC.
* __ppc_set_ppr_med_high: (libc)PowerPC.
* __ppc_set_ppr_med_low: (libc)PowerPC.
* __ppc_set_ppr_very_low: (libc)PowerPC.
* __ppc_yield: (libc)PowerPC.
* __riscv_flush_icache: (libc)RISC-V.
* __va_copy: (libc)Argument Macros.
* _exit: (libc)Termination Internals.
* _flushlbf: (libc)Flushing Buffers.
* _tolower: (libc)Case Conversion.
* _toupper: (libc)Case Conversion.
* a64l: (libc)Encode Binary Data.
* abort: (libc)Aborting a Program.
* abs: (libc)Absolute Value.
* accept: (libc)Accepting Connections.
* access: (libc)Testing File Access.
* acos: (libc)Inverse Trig Functions.
* acosf: (libc)Inverse Trig Functions.
* acosfN: (libc)Inverse Trig Functions.
* acosfNx: (libc)Inverse Trig Functions.
* acosh: (libc)Hyperbolic Functions.
* acoshf: (libc)Hyperbolic Functions.
* acoshfN: (libc)Hyperbolic Functions.
* acoshfNx: (libc)Hyperbolic Functions.
* acoshl: (libc)Hyperbolic Functions.
* acosl: (libc)Inverse Trig Functions.
* addmntent: (libc)mtab.
* addseverity: (libc)Adding Severity Classes.
* adjtime: (libc)High-Resolution Calendar.
* adjtimex: (libc)High-Resolution Calendar.
* aio_cancel64: (libc)Cancel AIO Operations.
* aio_cancel: (libc)Cancel AIO Operations.
* aio_error64: (libc)Status of AIO Operations.
* aio_error: (libc)Status of AIO Operations.
* aio_fsync64: (libc)Synchronizing AIO Operations.
* aio_fsync: (libc)Synchronizing AIO Operations.
* aio_init: (libc)Configuration of AIO.
* aio_read64: (libc)Asynchronous Reads/Writes.
* aio_read: (libc)Asynchronous Reads/Writes.
* aio_return64: (libc)Status of AIO Operations.
* aio_return: (libc)Status of AIO Operations.
* aio_suspend64: (libc)Synchronizing AIO Operations.
* aio_suspend: (libc)Synchronizing AIO Operations.
* aio_write64: (libc)Asynchronous Reads/Writes.
* aio_write: (libc)Asynchronous Reads/Writes.
* alarm: (libc)Setting an Alarm.
* aligned_alloc: (libc)Aligned Memory Blocks.
* alloca: (libc)Variable Size Automatic.
* alphasort64: (libc)Scanning Directory Content.
* alphasort: (libc)Scanning Directory Content.
* argp_error: (libc)Argp Helper Functions.
* argp_failure: (libc)Argp Helper Functions.
* argp_help: (libc)Argp Help.
* argp_parse: (libc)Argp.
* argp_state_help: (libc)Argp Helper Functions.
* argp_usage: (libc)Argp Helper Functions.
* argz_add: (libc)Argz Functions.
* argz_add_sep: (libc)Argz Functions.
* argz_append: (libc)Argz Functions.
* argz_count: (libc)Argz Functions.
* argz_create: (libc)Argz Functions.
* argz_create_sep: (libc)Argz Functions.
* argz_delete: (libc)Argz Functions.
* argz_extract: (libc)Argz Functions.
* argz_insert: (libc)Argz Functions.
* argz_next: (libc)Argz Functions.
* argz_replace: (libc)Argz Functions.
* argz_stringify: (libc)Argz Functions.
* asctime: (libc)Formatting Calendar Time.
* asctime_r: (libc)Formatting Calendar Time.
* asin: (libc)Inverse Trig Functions.
* asinf: (libc)Inverse Trig Functions.
* asinfN: (libc)Inverse Trig Functions.
* asinfNx: (libc)Inverse Trig Functions.
* asinh: (libc)Hyperbolic Functions.
* asinhf: (libc)Hyperbolic Functions.
* asinhfN: (libc)Hyperbolic Functions.
* asinhfNx: (libc)Hyperbolic Functions.
* asinhl: (libc)Hyperbolic Functions.
* asinl: (libc)Inverse Trig Functions.
* asprintf: (libc)Dynamic Output.
* assert: (libc)Consistency Checking.
* assert_perror: (libc)Consistency Checking.
* atan2: (libc)Inverse Trig Functions.
* atan2f: (libc)Inverse Trig Functions.
* atan2fN: (libc)Inverse Trig Functions.
* atan2fNx: (libc)Inverse Trig Functions.
* atan2l: (libc)Inverse Trig Functions.
* atan: (libc)Inverse Trig Functions.
* atanf: (libc)Inverse Trig Functions.
* atanfN: (libc)Inverse Trig Functions.
* atanfNx: (libc)Inverse Trig Functions.
* atanh: (libc)Hyperbolic Functions.
* atanhf: (libc)Hyperbolic Functions.
* atanhfN: (libc)Hyperbolic Functions.
* atanhfNx: (libc)Hyperbolic Functions.
* atanhl: (libc)Hyperbolic Functions.
* atanl: (libc)Inverse Trig Functions.
* atexit: (libc)Cleanups on Exit.
* atof: (libc)Parsing of Floats.
* atoi: (libc)Parsing of Integers.
* atol: (libc)Parsing of Integers.
* atoll: (libc)Parsing of Integers.
* backtrace: (libc)Backtraces.
* backtrace_symbols: (libc)Backtraces.
* backtrace_symbols_fd: (libc)Backtraces.
* basename: (libc)Finding Tokens in a String.
* basename: (libc)Finding Tokens in a String.
* bcmp: (libc)String/Array Comparison.
* bcopy: (libc)Copying Strings and Arrays.
* bind: (libc)Setting Address.
* bind_textdomain_codeset: (libc)Charset conversion in gettext.
* bindtextdomain: (libc)Locating gettext catalog.
* brk: (libc)Resizing the Data Segment.
* bsearch: (libc)Array Search Function.
* btowc: (libc)Converting a Character.
* bzero: (libc)Copying Strings and Arrays.
* cabs: (libc)Absolute Value.
* cabsf: (libc)Absolute Value.
* cabsfN: (libc)Absolute Value.
* cabsfNx: (libc)Absolute Value.
* cabsl: (libc)Absolute Value.
* cacos: (libc)Inverse Trig Functions.
* cacosf: (libc)Inverse Trig Functions.
* cacosfN: (libc)Inverse Trig Functions.
* cacosfNx: (libc)Inverse Trig Functions.
* cacosh: (libc)Hyperbolic Functions.
* cacoshf: (libc)Hyperbolic Functions.
* cacoshfN: (libc)Hyperbolic Functions.
* cacoshfNx: (libc)Hyperbolic Functions.
* cacoshl: (libc)Hyperbolic Functions.
* cacosl: (libc)Inverse Trig Functions.
* call_once: (libc)Call Once.
* calloc: (libc)Allocating Cleared Space.
* canonicalize: (libc)FP Bit Twiddling.
* canonicalize_file_name: (libc)Symbolic Links.
* canonicalizef: (libc)FP Bit Twiddling.
* canonicalizefN: (libc)FP Bit Twiddling.
* canonicalizefNx: (libc)FP Bit Twiddling.
* canonicalizel: (libc)FP Bit Twiddling.
* carg: (libc)Operations on Complex.
* cargf: (libc)Operations on Complex.
* cargfN: (libc)Operations on Complex.
* cargfNx: (libc)Operations on Complex.
* cargl: (libc)Operations on Complex.
* casin: (libc)Inverse Trig Functions.
* casinf: (libc)Inverse Trig Functions.
* casinfN: (libc)Inverse Trig Functions.
* casinfNx: (libc)Inverse Trig Functions.
* casinh: (libc)Hyperbolic Functions.
* casinhf: (libc)Hyperbolic Functions.
* casinhfN: (libc)Hyperbolic Functions.
* casinhfNx: (libc)Hyperbolic Functions.
* casinhl: (libc)Hyperbolic Functions.
* casinl: (libc)Inverse Trig Functions.
* catan: (libc)Inverse Trig Functions.
* catanf: (libc)Inverse Trig Functions.
* catanfN: (libc)Inverse Trig Functions.
* catanfNx: (libc)Inverse Trig Functions.
* catanh: (libc)Hyperbolic Functions.
* catanhf: (libc)Hyperbolic Functions.
* catanhfN: (libc)Hyperbolic Functions.
* catanhfNx: (libc)Hyperbolic Functions.
* catanhl: (libc)Hyperbolic Functions.
* catanl: (libc)Inverse Trig Functions.
* catclose: (libc)The catgets Functions.
* catgets: (libc)The catgets Functions.
* catopen: (libc)The catgets Functions.
* cbrt: (libc)Exponents and Logarithms.
* cbrtf: (libc)Exponents and Logarithms.
* cbrtfN: (libc)Exponents and Logarithms.
* cbrtfNx: (libc)Exponents and Logarithms.
* cbrtl: (libc)Exponents and Logarithms.
* ccos: (libc)Trig Functions.
* ccosf: (libc)Trig Functions.
* ccosfN: (libc)Trig Functions.
* ccosfNx: (libc)Trig Functions.
* ccosh: (libc)Hyperbolic Functions.
* ccoshf: (libc)Hyperbolic Functions.
* ccoshfN: (libc)Hyperbolic Functions.
* ccoshfNx: (libc)Hyperbolic Functions.
* ccoshl: (libc)Hyperbolic Functions.
* ccosl: (libc)Trig Functions.
* ceil: (libc)Rounding Functions.
* ceilf: (libc)Rounding Functions.
* ceilfN: (libc)Rounding Functions.
* ceilfNx: (libc)Rounding Functions.
* ceill: (libc)Rounding Functions.
* cexp: (libc)Exponents and Logarithms.
* cexpf: (libc)Exponents and Logarithms.
* cexpfN: (libc)Exponents and Logarithms.
* cexpfNx: (libc)Exponents and Logarithms.
* cexpl: (libc)Exponents and Logarithms.
* cfgetispeed: (libc)Line Speed.
* cfgetospeed: (libc)Line Speed.
* cfmakeraw: (libc)Noncanonical Input.
* cfsetispeed: (libc)Line Speed.
* cfsetospeed: (libc)Line Speed.
* cfsetspeed: (libc)Line Speed.
* chdir: (libc)Working Directory.
* chmod: (libc)Setting Permissions.
* chown: (libc)File Owner.
* cimag: (libc)Operations on Complex.
* cimagf: (libc)Operations on Complex.
* cimagfN: (libc)Operations on Complex.
* cimagfNx: (libc)Operations on Complex.
* cimagl: (libc)Operations on Complex.
* clearenv: (libc)Environment Access.
* clearerr: (libc)Error Recovery.
* clearerr_unlocked: (libc)Error Recovery.
* clock: (libc)CPU Time.
* clog10: (libc)Exponents and Logarithms.
* clog10f: (libc)Exponents and Logarithms.
* clog10fN: (libc)Exponents and Logarithms.
* clog10fNx: (libc)Exponents and Logarithms.
* clog10l: (libc)Exponents and Logarithms.
* clog: (libc)Exponents and Logarithms.
* clogf: (libc)Exponents and Logarithms.
* clogfN: (libc)Exponents and Logarithms.
* clogfNx: (libc)Exponents and Logarithms.
* clogl: (libc)Exponents and Logarithms.
* close: (libc)Opening and Closing Files.
* closedir: (libc)Reading/Closing Directory.
* closelog: (libc)closelog.
* cnd_broadcast: (libc)ISO C Condition Variables.
* cnd_destroy: (libc)ISO C Condition Variables.
* cnd_init: (libc)ISO C Condition Variables.
* cnd_signal: (libc)ISO C Condition Variables.
* cnd_timedwait: (libc)ISO C Condition Variables.
* cnd_wait: (libc)ISO C Condition Variables.
* confstr: (libc)String Parameters.
* conj: (libc)Operations on Complex.
* conjf: (libc)Operations on Complex.
* conjfN: (libc)Operations on Complex.
* conjfNx: (libc)Operations on Complex.
* conjl: (libc)Operations on Complex.
* connect: (libc)Connecting.
* copy_file_range: (libc)Copying File Data.
* copysign: (libc)FP Bit Twiddling.
* copysignf: (libc)FP Bit Twiddling.
* copysignfN: (libc)FP Bit Twiddling.
* copysignfNx: (libc)FP Bit Twiddling.
* copysignl: (libc)FP Bit Twiddling.
* cos: (libc)Trig Functions.
* cosf: (libc)Trig Functions.
* cosfN: (libc)Trig Functions.
* cosfNx: (libc)Trig Functions.
* cosh: (libc)Hyperbolic Functions.
* coshf: (libc)Hyperbolic Functions.
* coshfN: (libc)Hyperbolic Functions.
* coshfNx: (libc)Hyperbolic Functions.
* coshl: (libc)Hyperbolic Functions.
* cosl: (libc)Trig Functions.
* cpow: (libc)Exponents and Logarithms.
* cpowf: (libc)Exponents and Logarithms.
* cpowfN: (libc)Exponents and Logarithms.
* cpowfNx: (libc)Exponents and Logarithms.
* cpowl: (libc)Exponents and Logarithms.
* cproj: (libc)Operations on Complex.
* cprojf: (libc)Operations on Complex.
* cprojfN: (libc)Operations on Complex.
* cprojfNx: (libc)Operations on Complex.
* cprojl: (libc)Operations on Complex.
* creal: (libc)Operations on Complex.
* crealf: (libc)Operations on Complex.
* crealfN: (libc)Operations on Complex.
* crealfNx: (libc)Operations on Complex.
* creall: (libc)Operations on Complex.
* creat64: (libc)Opening and Closing Files.
* creat: (libc)Opening and Closing Files.
* crypt: (libc)Passphrase Storage.
* crypt_r: (libc)Passphrase Storage.
* csin: (libc)Trig Functions.
* csinf: (libc)Trig Functions.
* csinfN: (libc)Trig Functions.
* csinfNx: (libc)Trig Functions.
* csinh: (libc)Hyperbolic Functions.
* csinhf: (libc)Hyperbolic Functions.
* csinhfN: (libc)Hyperbolic Functions.
* csinhfNx: (libc)Hyperbolic Functions.
* csinhl: (libc)Hyperbolic Functions.
* csinl: (libc)Trig Functions.
* csqrt: (libc)Exponents and Logarithms.
* csqrtf: (libc)Exponents and Logarithms.
* csqrtfN: (libc)Exponents and Logarithms.
* csqrtfNx: (libc)Exponents and Logarithms.
* csqrtl: (libc)Exponents and Logarithms.
* ctan: (libc)Trig Functions.
* ctanf: (libc)Trig Functions.
* ctanfN: (libc)Trig Functions.
* ctanfNx: (libc)Trig Functions.
* ctanh: (libc)Hyperbolic Functions.
* ctanhf: (libc)Hyperbolic Functions.
* ctanhfN: (libc)Hyperbolic Functions.
* ctanhfNx: (libc)Hyperbolic Functions.
* ctanhl: (libc)Hyperbolic Functions.
* ctanl: (libc)Trig Functions.
* ctermid: (libc)Identifying the Terminal.
* ctime: (libc)Formatting Calendar Time.
* ctime_r: (libc)Formatting Calendar Time.
* cuserid: (libc)Who Logged In.
* daddl: (libc)Misc FP Arithmetic.
* dcgettext: (libc)Translation with gettext.
* dcngettext: (libc)Advanced gettext functions.
* ddivl: (libc)Misc FP Arithmetic.
* dgettext: (libc)Translation with gettext.
* difftime: (libc)Elapsed Time.
* dirfd: (libc)Opening a Directory.
* dirname: (libc)Finding Tokens in a String.
* div: (libc)Integer Division.
* dmull: (libc)Misc FP Arithmetic.
* dngettext: (libc)Advanced gettext functions.
* drand48: (libc)SVID Random.
* drand48_r: (libc)SVID Random.
* drem: (libc)Remainder Functions.
* dremf: (libc)Remainder Functions.
* dreml: (libc)Remainder Functions.
* dsubl: (libc)Misc FP Arithmetic.
* dup2: (libc)Duplicating Descriptors.
* dup: (libc)Duplicating Descriptors.
* ecvt: (libc)System V Number Conversion.
* ecvt_r: (libc)System V Number Conversion.
* endfsent: (libc)fstab.
* endgrent: (libc)Scanning All Groups.
* endhostent: (libc)Host Names.
* endmntent: (libc)mtab.
* endnetent: (libc)Networks Database.
* endnetgrent: (libc)Lookup Netgroup.
* endprotoent: (libc)Protocols Database.
* endpwent: (libc)Scanning All Users.
* endservent: (libc)Services Database.
* endutent: (libc)Manipulating the Database.
* endutxent: (libc)XPG Functions.
* envz_add: (libc)Envz Functions.
* envz_entry: (libc)Envz Functions.
* envz_get: (libc)Envz Functions.
* envz_merge: (libc)Envz Functions.
* envz_remove: (libc)Envz Functions.
* envz_strip: (libc)Envz Functions.
* erand48: (libc)SVID Random.
* erand48_r: (libc)SVID Random.
* erf: (libc)Special Functions.
* erfc: (libc)Special Functions.
* erfcf: (libc)Special Functions.
* erfcfN: (libc)Special Functions.
* erfcfNx: (libc)Special Functions.
* erfcl: (libc)Special Functions.
* erff: (libc)Special Functions.
* erffN: (libc)Special Functions.
* erffNx: (libc)Special Functions.
* erfl: (libc)Special Functions.
* err: (libc)Error Messages.
* errno: (libc)Checking for Errors.
* error: (libc)Error Messages.
* error_at_line: (libc)Error Messages.
* errx: (libc)Error Messages.
* execl: (libc)Executing a File.
* execle: (libc)Executing a File.
* execlp: (libc)Executing a File.
* execv: (libc)Executing a File.
* execve: (libc)Executing a File.
* execvp: (libc)Executing a File.
* exit: (libc)Normal Termination.
* exp10: (libc)Exponents and Logarithms.
* exp10f: (libc)Exponents and Logarithms.
* exp10fN: (libc)Exponents and Logarithms.
* exp10fNx: (libc)Exponents and Logarithms.
* exp10l: (libc)Exponents and Logarithms.
* exp2: (libc)Exponents and Logarithms.
* exp2f: (libc)Exponents and Logarithms.
* exp2fN: (libc)Exponents and Logarithms.
* exp2fNx: (libc)Exponents and Logarithms.
* exp2l: (libc)Exponents and Logarithms.
* exp: (libc)Exponents and Logarithms.
* expf: (libc)Exponents and Logarithms.
* expfN: (libc)Exponents and Logarithms.
* expfNx: (libc)Exponents and Logarithms.
* expl: (libc)Exponents and Logarithms.
* explicit_bzero: (libc)Erasing Sensitive Data.
* expm1: (libc)Exponents and Logarithms.
* expm1f: (libc)Exponents and Logarithms.
* expm1fN: (libc)Exponents and Logarithms.
* expm1fNx: (libc)Exponents and Logarithms.
* expm1l: (libc)Exponents and Logarithms.
* fMaddfN: (libc)Misc FP Arithmetic.
* fMaddfNx: (libc)Misc FP Arithmetic.
* fMdivfN: (libc)Misc FP Arithmetic.
* fMdivfNx: (libc)Misc FP Arithmetic.
* fMmulfN: (libc)Misc FP Arithmetic.
* fMmulfNx: (libc)Misc FP Arithmetic.
* fMsubfN: (libc)Misc FP Arithmetic.
* fMsubfNx: (libc)Misc FP Arithmetic.
* fMxaddfN: (libc)Misc FP Arithmetic.
* fMxaddfNx: (libc)Misc FP Arithmetic.
* fMxdivfN: (libc)Misc FP Arithmetic.
* fMxdivfNx: (libc)Misc FP Arithmetic.
* fMxmulfN: (libc)Misc FP Arithmetic.
* fMxmulfNx: (libc)Misc FP Arithmetic.
* fMxsubfN: (libc)Misc FP Arithmetic.
* fMxsubfNx: (libc)Misc FP Arithmetic.
* fabs: (libc)Absolute Value.
* fabsf: (libc)Absolute Value.
* fabsfN: (libc)Absolute Value.
* fabsfNx: (libc)Absolute Value.
* fabsl: (libc)Absolute Value.
* fadd: (libc)Misc FP Arithmetic.
* faddl: (libc)Misc FP Arithmetic.
* fchdir: (libc)Working Directory.
* fchmod: (libc)Setting Permissions.
* fchown: (libc)File Owner.
* fclose: (libc)Closing Streams.
* fcloseall: (libc)Closing Streams.
* fcntl: (libc)Control Operations.
* fcvt: (libc)System V Number Conversion.
* fcvt_r: (libc)System V Number Conversion.
* fdatasync: (libc)Synchronizing I/O.
* fdim: (libc)Misc FP Arithmetic.
* fdimf: (libc)Misc FP Arithmetic.
* fdimfN: (libc)Misc FP Arithmetic.
* fdimfNx: (libc)Misc FP Arithmetic.
* fdiml: (libc)Misc FP Arithmetic.
* fdiv: (libc)Misc FP Arithmetic.
* fdivl: (libc)Misc FP Arithmetic.
* fdopen: (libc)Descriptors and Streams.
* fdopendir: (libc)Opening a Directory.
* feclearexcept: (libc)Status bit operations.
* fedisableexcept: (libc)Control Functions.
* feenableexcept: (libc)Control Functions.
* fegetenv: (libc)Control Functions.
* fegetexcept: (libc)Control Functions.
* fegetexceptflag: (libc)Status bit operations.
* fegetmode: (libc)Control Functions.
* fegetround: (libc)Rounding.
* feholdexcept: (libc)Control Functions.
* feof: (libc)EOF and Errors.
* feof_unlocked: (libc)EOF and Errors.
* feraiseexcept: (libc)Status bit operations.
* ferror: (libc)EOF and Errors.
* ferror_unlocked: (libc)EOF and Errors.
* fesetenv: (libc)Control Functions.
* fesetexcept: (libc)Status bit operations.
* fesetexceptflag: (libc)Status bit operations.
* fesetmode: (libc)Control Functions.
* fesetround: (libc)Rounding.
* fetestexcept: (libc)Status bit operations.
* fetestexceptflag: (libc)Status bit operations.
* feupdateenv: (libc)Control Functions.
* fflush: (libc)Flushing Buffers.
* fflush_unlocked: (libc)Flushing Buffers.
* fgetc: (libc)Character Input.
* fgetc_unlocked: (libc)Character Input.
* fgetgrent: (libc)Scanning All Groups.
* fgetgrent_r: (libc)Scanning All Groups.
* fgetpos64: (libc)Portable Positioning.
* fgetpos: (libc)Portable Positioning.
* fgetpwent: (libc)Scanning All Users.
* fgetpwent_r: (libc)Scanning All Users.
* fgets: (libc)Line Input.
* fgets_unlocked: (libc)Line Input.
* fgetwc: (libc)Character Input.
* fgetwc_unlocked: (libc)Character Input.
* fgetws: (libc)Line Input.
* fgetws_unlocked: (libc)Line Input.
* fileno: (libc)Descriptors and Streams.
* fileno_unlocked: (libc)Descriptors and Streams.
* finite: (libc)Floating Point Classes.
* finitef: (libc)Floating Point Classes.
* finitel: (libc)Floating Point Classes.
* flockfile: (libc)Streams and Threads.
* floor: (libc)Rounding Functions.
* floorf: (libc)Rounding Functions.
* floorfN: (libc)Rounding Functions.
* floorfNx: (libc)Rounding Functions.
* floorl: (libc)Rounding Functions.
* fma: (libc)Misc FP Arithmetic.
* fmaf: (libc)Misc FP Arithmetic.
* fmafN: (libc)Misc FP Arithmetic.
* fmafNx: (libc)Misc FP Arithmetic.
* fmal: (libc)Misc FP Arithmetic.
* fmax: (libc)Misc FP Arithmetic.
* fmaxf: (libc)Misc FP Arithmetic.
* fmaxfN: (libc)Misc FP Arithmetic.
* fmaxfNx: (libc)Misc FP Arithmetic.
* fmaxl: (libc)Misc FP Arithmetic.
* fmaxmag: (libc)Misc FP Arithmetic.
* fmaxmagf: (libc)Misc FP Arithmetic.
* fmaxmagfN: (libc)Misc FP Arithmetic.
* fmaxmagfNx: (libc)Misc FP Arithmetic.
* fmaxmagl: (libc)Misc FP Arithmetic.
* fmemopen: (libc)String Streams.
* fmin: (libc)Misc FP Arithmetic.
* fminf: (libc)Misc FP Arithmetic.
* fminfN: (libc)Misc FP Arithmetic.
* fminfNx: (libc)Misc FP Arithmetic.
* fminl: (libc)Misc FP Arithmetic.
* fminmag: (libc)Misc FP Arithmetic.
* fminmagf: (libc)Misc FP Arithmetic.
* fminmagfN: (libc)Misc FP Arithmetic.
* fminmagfNx: (libc)Misc FP Arithmetic.
* fminmagl: (libc)Misc FP Arithmetic.
* fmod: (libc)Remainder Functions.
* fmodf: (libc)Remainder Functions.
* fmodfN: (libc)Remainder Functions.
* fmodfNx: (libc)Remainder Functions.
* fmodl: (libc)Remainder Functions.
* fmtmsg: (libc)Printing Formatted Messages.
* fmul: (libc)Misc FP Arithmetic.
* fmull: (libc)Misc FP Arithmetic.
* fnmatch: (libc)Wildcard Matching.
* fopen64: (libc)Opening Streams.
* fopen: (libc)Opening Streams.
* fopencookie: (libc)Streams and Cookies.
* fork: (libc)Creating a Process.
* forkpty: (libc)Pseudo-Terminal Pairs.
* fpathconf: (libc)Pathconf.
* fpclassify: (libc)Floating Point Classes.
* fprintf: (libc)Formatted Output Functions.
* fputc: (libc)Simple Output.
* fputc_unlocked: (libc)Simple Output.
* fputs: (libc)Simple Output.
* fputs_unlocked: (libc)Simple Output.
* fputwc: (libc)Simple Output.
* fputwc_unlocked: (libc)Simple Output.
* fputws: (libc)Simple Output.
* fputws_unlocked: (libc)Simple Output.
* fread: (libc)Block Input/Output.
* fread_unlocked: (libc)Block Input/Output.
* free: (libc)Freeing after Malloc.
* freopen64: (libc)Opening Streams.
* freopen: (libc)Opening Streams.
* frexp: (libc)Normalization Functions.
* frexpf: (libc)Normalization Functions.
* frexpfN: (libc)Normalization Functions.
* frexpfNx: (libc)Normalization Functions.
* frexpl: (libc)Normalization Functions.
* fromfp: (libc)Rounding Functions.
* fromfpf: (libc)Rounding Functions.
* fromfpfN: (libc)Rounding Functions.
* fromfpfNx: (libc)Rounding Functions.
* fromfpl: (libc)Rounding Functions.
* fromfpx: (libc)Rounding Functions.
* fromfpxf: (libc)Rounding Functions.
* fromfpxfN: (libc)Rounding Functions.
* fromfpxfNx: (libc)Rounding Functions.
* fromfpxl: (libc)Rounding Functions.
* fscanf: (libc)Formatted Input Functions.
* fseek: (libc)File Positioning.
* fseeko64: (libc)File Positioning.
* fseeko: (libc)File Positioning.
* fsetpos64: (libc)Portable Positioning.
* fsetpos: (libc)Portable Positioning.
* fstat64: (libc)Reading Attributes.
* fstat: (libc)Reading Attributes.
* fsub: (libc)Misc FP Arithmetic.
* fsubl: (libc)Misc FP Arithmetic.
* fsync: (libc)Synchronizing I/O.
* ftell: (libc)File Positioning.
* ftello64: (libc)File Positioning.
* ftello: (libc)File Positioning.
* ftruncate64: (libc)File Size.
* ftruncate: (libc)File Size.
* ftrylockfile: (libc)Streams and Threads.
* ftw64: (libc)Working with Directory Trees.
* ftw: (libc)Working with Directory Trees.
* funlockfile: (libc)Streams and Threads.
* futimes: (libc)File Times.
* fwide: (libc)Streams and I18N.
* fwprintf: (libc)Formatted Output Functions.
* fwrite: (libc)Block Input/Output.
* fwrite_unlocked: (libc)Block Input/Output.
* fwscanf: (libc)Formatted Input Functions.
* gamma: (libc)Special Functions.
* gammaf: (libc)Special Functions.
* gammal: (libc)Special Functions.
* gcvt: (libc)System V Number Conversion.
* get_avphys_pages: (libc)Query Memory Parameters.
* get_current_dir_name: (libc)Working Directory.
* get_nprocs: (libc)Processor Resources.
* get_nprocs_conf: (libc)Processor Resources.
* get_phys_pages: (libc)Query Memory Parameters.
* getauxval: (libc)Auxiliary Vector.
* getc: (libc)Character Input.
* getc_unlocked: (libc)Character Input.
* getchar: (libc)Character Input.
* getchar_unlocked: (libc)Character Input.
* getcontext: (libc)System V contexts.
* getcpu: (libc)CPU Affinity.
* getcwd: (libc)Working Directory.
* getdate: (libc)General Time String Parsing.
* getdate_r: (libc)General Time String Parsing.
* getdelim: (libc)Line Input.
* getdents64: (libc)Low-level Directory Access.
* getdomainnname: (libc)Host Identification.
* getegid: (libc)Reading Persona.
* getentropy: (libc)Unpredictable Bytes.
* getenv: (libc)Environment Access.
* geteuid: (libc)Reading Persona.
* getfsent: (libc)fstab.
* getfsfile: (libc)fstab.
* getfsspec: (libc)fstab.
* getgid: (libc)Reading Persona.
* getgrent: (libc)Scanning All Groups.
* getgrent_r: (libc)Scanning All Groups.
* getgrgid: (libc)Lookup Group.
* getgrgid_r: (libc)Lookup Group.
* getgrnam: (libc)Lookup Group.
* getgrnam_r: (libc)Lookup Group.
* getgrouplist: (libc)Setting Groups.
* getgroups: (libc)Reading Persona.
* gethostbyaddr: (libc)Host Names.
* gethostbyaddr_r: (libc)Host Names.
* gethostbyname2: (libc)Host Names.
* gethostbyname2_r: (libc)Host Names.
* gethostbyname: (libc)Host Names.
* gethostbyname_r: (libc)Host Names.
* gethostent: (libc)Host Names.
* gethostid: (libc)Host Identification.
* gethostname: (libc)Host Identification.
* getitimer: (libc)Setting an Alarm.
* getline: (libc)Line Input.
* getloadavg: (libc)Processor Resources.
* getlogin: (libc)Who Logged In.
* getmntent: (libc)mtab.
* getmntent_r: (libc)mtab.
* getnetbyaddr: (libc)Networks Database.
* getnetbyname: (libc)Networks Database.
* getnetent: (libc)Networks Database.
* getnetgrent: (libc)Lookup Netgroup.
* getnetgrent_r: (libc)Lookup Netgroup.
* getopt: (libc)Using Getopt.
* getopt_long: (libc)Getopt Long Options.
* getopt_long_only: (libc)Getopt Long Options.
* getpagesize: (libc)Query Memory Parameters.
* getpass: (libc)getpass.
* getpayload: (libc)FP Bit Twiddling.
* getpayloadf: (libc)FP Bit Twiddling.
* getpayloadfN: (libc)FP Bit Twiddling.
* getpayloadfNx: (libc)FP Bit Twiddling.
* getpayloadl: (libc)FP Bit Twiddling.
* getpeername: (libc)Who is Connected.
* getpgid: (libc)Process Group Functions.
* getpgrp: (libc)Process Group Functions.
* getpid: (libc)Process Identification.
* getppid: (libc)Process Identification.
* getpriority: (libc)Traditional Scheduling Functions.
* getprotobyname: (libc)Protocols Database.
* getprotobynumber: (libc)Protocols Database.
* getprotoent: (libc)Protocols Database.
* getpt: (libc)Allocation.
* getpwent: (libc)Scanning All Users.
* getpwent_r: (libc)Scanning All Users.
* getpwnam: (libc)Lookup User.
* getpwnam_r: (libc)Lookup User.
* getpwuid: (libc)Lookup User.
* getpwuid_r: (libc)Lookup User.
* getrandom: (libc)Unpredictable Bytes.
* getrlimit64: (libc)Limits on Resources.
* getrlimit: (libc)Limits on Resources.
* getrusage: (libc)Resource Usage.
* gets: (libc)Line Input.
* getservbyname: (libc)Services Database.
* getservbyport: (libc)Services Database.
* getservent: (libc)Services Database.
* getsid: (libc)Process Group Functions.
* getsockname: (libc)Reading Address.
* getsockopt: (libc)Socket Option Functions.
* getsubopt: (libc)Suboptions.
* gettext: (libc)Translation with gettext.
* gettid: (libc)Process Identification.
* gettimeofday: (libc)High-Resolution Calendar.
* getuid: (libc)Reading Persona.
* getumask: (libc)Setting Permissions.
* getutent: (libc)Manipulating the Database.
* getutent_r: (libc)Manipulating the Database.
* getutid: (libc)Manipulating the Database.
* getutid_r: (libc)Manipulating the Database.
* getutline: (libc)Manipulating the Database.
* getutline_r: (libc)Manipulating the Database.
* getutmp: (libc)XPG Functions.
* getutmpx: (libc)XPG Functions.
* getutxent: (libc)XPG Functions.
* getutxid: (libc)XPG Functions.
* getutxline: (libc)XPG Functions.
* getw: (libc)Character Input.
* getwc: (libc)Character Input.
* getwc_unlocked: (libc)Character Input.
* getwchar: (libc)Character Input.
* getwchar_unlocked: (libc)Character Input.
* getwd: (libc)Working Directory.
* glob64: (libc)Calling Glob.
* glob: (libc)Calling Glob.
* globfree64: (libc)More Flags for Globbing.
* globfree: (libc)More Flags for Globbing.
* gmtime: (libc)Broken-down Time.
* gmtime_r: (libc)Broken-down Time.
* grantpt: (libc)Allocation.
* gsignal: (libc)Signaling Yourself.
* gtty: (libc)BSD Terminal Modes.
* hasmntopt: (libc)mtab.
* hcreate: (libc)Hash Search Function.
* hcreate_r: (libc)Hash Search Function.
* hdestroy: (libc)Hash Search Function.
* hdestroy_r: (libc)Hash Search Function.
* hsearch: (libc)Hash Search Function.
* hsearch_r: (libc)Hash Search Function.
* htonl: (libc)Byte Order.
* htons: (libc)Byte Order.
* hypot: (libc)Exponents and Logarithms.
* hypotf: (libc)Exponents and Logarithms.
* hypotfN: (libc)Exponents and Logarithms.
* hypotfNx: (libc)Exponents and Logarithms.
* hypotl: (libc)Exponents and Logarithms.
* iconv: (libc)Generic Conversion Interface.
* iconv_close: (libc)Generic Conversion Interface.
* iconv_open: (libc)Generic Conversion Interface.
* if_freenameindex: (libc)Interface Naming.
* if_indextoname: (libc)Interface Naming.
* if_nameindex: (libc)Interface Naming.
* if_nametoindex: (libc)Interface Naming.
* ilogb: (libc)Exponents and Logarithms.
* ilogbf: (libc)Exponents and Logarithms.
* ilogbfN: (libc)Exponents and Logarithms.
* ilogbfNx: (libc)Exponents and Logarithms.
* ilogbl: (libc)Exponents and Logarithms.
* imaxabs: (libc)Absolute Value.
* imaxdiv: (libc)Integer Division.
* in6addr_any: (libc)Host Address Data Type.
* in6addr_loopback: (libc)Host Address Data Type.
* index: (libc)Search Functions.
* inet_addr: (libc)Host Address Functions.
* inet_aton: (libc)Host Address Functions.
* inet_lnaof: (libc)Host Address Functions.
* inet_makeaddr: (libc)Host Address Functions.
* inet_netof: (libc)Host Address Functions.
* inet_network: (libc)Host Address Functions.
* inet_ntoa: (libc)Host Address Functions.
* inet_ntop: (libc)Host Address Functions.
* inet_pton: (libc)Host Address Functions.
* initgroups: (libc)Setting Groups.
* initstate: (libc)BSD Random.
* initstate_r: (libc)BSD Random.
* innetgr: (libc)Netgroup Membership.
* ioctl: (libc)IOCTLs.
* isalnum: (libc)Classification of Characters.
* isalpha: (libc)Classification of Characters.
* isascii: (libc)Classification of Characters.
* isatty: (libc)Is It a Terminal.
* isblank: (libc)Classification of Characters.
* iscanonical: (libc)Floating Point Classes.
* iscntrl: (libc)Classification of Characters.
* isdigit: (libc)Classification of Characters.
* iseqsig: (libc)FP Comparison Functions.
* isfinite: (libc)Floating Point Classes.
* isgraph: (libc)Classification of Characters.
* isgreater: (libc)FP Comparison Functions.
* isgreaterequal: (libc)FP Comparison Functions.
* isinf: (libc)Floating Point Classes.
* isinff: (libc)Floating Point Classes.
* isinfl: (libc)Floating Point Classes.
* isless: (libc)FP Comparison Functions.
* islessequal: (libc)FP Comparison Functions.
* islessgreater: (libc)FP Comparison Functions.
* islower: (libc)Classification of Characters.
* isnan: (libc)Floating Point Classes.
* isnan: (libc)Floating Point Classes.
* isnanf: (libc)Floating Point Classes.
* isnanl: (libc)Floating Point Classes.
* isnormal: (libc)Floating Point Classes.
* isprint: (libc)Classification of Characters.
* ispunct: (libc)Classification of Characters.
* issignaling: (libc)Floating Point Classes.
* isspace: (libc)Classification of Characters.
* issubnormal: (libc)Floating Point Classes.
* isunordered: (libc)FP Comparison Functions.
* isupper: (libc)Classification of Characters.
* iswalnum: (libc)Classification of Wide Characters.
* iswalpha: (libc)Classification of Wide Characters.
* iswblank: (libc)Classification of Wide Characters.
* iswcntrl: (libc)Classification of Wide Characters.
* iswctype: (libc)Classification of Wide Characters.
* iswdigit: (libc)Classification of Wide Characters.
* iswgraph: (libc)Classification of Wide Characters.
* iswlower: (libc)Classification of Wide Characters.
* iswprint: (libc)Classification of Wide Characters.
* iswpunct: (libc)Classification of Wide Characters.
* iswspace: (libc)Classification of Wide Characters.
* iswupper: (libc)Classification of Wide Characters.
* iswxdigit: (libc)Classification of Wide Characters.
* isxdigit: (libc)Classification of Characters.
* iszero: (libc)Floating Point Classes.
* j0: (libc)Special Functions.
* j0f: (libc)Special Functions.
* j0fN: (libc)Special Functions.
* j0fNx: (libc)Special Functions.
* j0l: (libc)Special Functions.
* j1: (libc)Special Functions.
* j1f: (libc)Special Functions.
* j1fN: (libc)Special Functions.
* j1fNx: (libc)Special Functions.
* j1l: (libc)Special Functions.
* jn: (libc)Special Functions.
* jnf: (libc)Special Functions.
* jnfN: (libc)Special Functions.
* jnfNx: (libc)Special Functions.
* jnl: (libc)Special Functions.
* jrand48: (libc)SVID Random.
* jrand48_r: (libc)SVID Random.
* kill: (libc)Signaling Another Process.
* killpg: (libc)Signaling Another Process.
* l64a: (libc)Encode Binary Data.
* labs: (libc)Absolute Value.
* lcong48: (libc)SVID Random.
* lcong48_r: (libc)SVID Random.
* ldexp: (libc)Normalization Functions.
* ldexpf: (libc)Normalization Functions.
* ldexpfN: (libc)Normalization Functions.
* ldexpfNx: (libc)Normalization Functions.
* ldexpl: (libc)Normalization Functions.
* ldiv: (libc)Integer Division.
* lfind: (libc)Array Search Function.
* lgamma: (libc)Special Functions.
* lgamma_r: (libc)Special Functions.
* lgammaf: (libc)Special Functions.
* lgammafN: (libc)Special Functions.
* lgammafN_r: (libc)Special Functions.
* lgammafNx: (libc)Special Functions.
* lgammafNx_r: (libc)Special Functions.
* lgammaf_r: (libc)Special Functions.
* lgammal: (libc)Special Functions.
* lgammal_r: (libc)Special Functions.
* link: (libc)Hard Links.
* linkat: (libc)Hard Links.
* lio_listio64: (libc)Asynchronous Reads/Writes.
* lio_listio: (libc)Asynchronous Reads/Writes.
* listen: (libc)Listening.
* llabs: (libc)Absolute Value.
* lldiv: (libc)Integer Division.
* llogb: (libc)Exponents and Logarithms.
* llogbf: (libc)Exponents and Logarithms.
* llogbfN: (libc)Exponents and Logarithms.
* llogbfNx: (libc)Exponents and Logarithms.
* llogbl: (libc)Exponents and Logarithms.
* llrint: (libc)Rounding Functions.
* llrintf: (libc)Rounding Functions.
* llrintfN: (libc)Rounding Functions.
* llrintfNx: (libc)Rounding Functions.
* llrintl: (libc)Rounding Functions.
* llround: (libc)Rounding Functions.
* llroundf: (libc)Rounding Functions.
* llroundfN: (libc)Rounding Functions.
* llroundfNx: (libc)Rounding Functions.
* llroundl: (libc)Rounding Functions.
* localeconv: (libc)The Lame Way to Locale Data.
* localtime: (libc)Broken-down Time.
* localtime_r: (libc)Broken-down Time.
* log10: (libc)Exponents and Logarithms.
* log10f: (libc)Exponents and Logarithms.
* log10fN: (libc)Exponents and Logarithms.
* log10fNx: (libc)Exponents and Logarithms.
* log10l: (libc)Exponents and Logarithms.
* log1p: (libc)Exponents and Logarithms.
* log1pf: (libc)Exponents and Logarithms.
* log1pfN: (libc)Exponents and Logarithms.
* log1pfNx: (libc)Exponents and Logarithms.
* log1pl: (libc)Exponents and Logarithms.
* log2: (libc)Exponents and Logarithms.
* log2f: (libc)Exponents and Logarithms.
* log2fN: (libc)Exponents and Logarithms.
* log2fNx: (libc)Exponents and Logarithms.
* log2l: (libc)Exponents and Logarithms.
* log: (libc)Exponents and Logarithms.
* logb: (libc)Exponents and Logarithms.
* logbf: (libc)Exponents and Logarithms.
* logbfN: (libc)Exponents and Logarithms.
* logbfNx: (libc)Exponents and Logarithms.
* logbl: (libc)Exponents and Logarithms.
* logf: (libc)Exponents and Logarithms.
* logfN: (libc)Exponents and Logarithms.
* logfNx: (libc)Exponents and Logarithms.
* login: (libc)Logging In and Out.
* login_tty: (libc)Logging In and Out.
* logl: (libc)Exponents and Logarithms.
* logout: (libc)Logging In and Out.
* logwtmp: (libc)Logging In and Out.
* longjmp: (libc)Non-Local Details.
* lrand48: (libc)SVID Random.
* lrand48_r: (libc)SVID Random.
* lrint: (libc)Rounding Functions.
* lrintf: (libc)Rounding Functions.
* lrintfN: (libc)Rounding Functions.
* lrintfNx: (libc)Rounding Functions.
* lrintl: (libc)Rounding Functions.
* lround: (libc)Rounding Functions.
* lroundf: (libc)Rounding Functions.
* lroundfN: (libc)Rounding Functions.
* lroundfNx: (libc)Rounding Functions.
* lroundl: (libc)Rounding Functions.
* lsearch: (libc)Array Search Function.
* lseek64: (libc)File Position Primitive.
* lseek: (libc)File Position Primitive.
* lstat64: (libc)Reading Attributes.
* lstat: (libc)Reading Attributes.
* lutimes: (libc)File Times.
* madvise: (libc)Memory-mapped I/O.
* makecontext: (libc)System V contexts.
* mallinfo: (libc)Statistics of Malloc.
* malloc: (libc)Basic Allocation.
* mallopt: (libc)Malloc Tunable Parameters.
* mblen: (libc)Non-reentrant Character Conversion.
* mbrlen: (libc)Converting a Character.
* mbrtowc: (libc)Converting a Character.
* mbsinit: (libc)Keeping the state.
* mbsnrtowcs: (libc)Converting Strings.
* mbsrtowcs: (libc)Converting Strings.
* mbstowcs: (libc)Non-reentrant String Conversion.
* mbtowc: (libc)Non-reentrant Character Conversion.
* mcheck: (libc)Heap Consistency Checking.
* memalign: (libc)Aligned Memory Blocks.
* memccpy: (libc)Copying Strings and Arrays.
* memchr: (libc)Search Functions.
* memcmp: (libc)String/Array Comparison.
* memcpy: (libc)Copying Strings and Arrays.
* memfd_create: (libc)Memory-mapped I/O.
* memfrob: (libc)Obfuscating Data.
* memmem: (libc)Search Functions.
* memmove: (libc)Copying Strings and Arrays.
* mempcpy: (libc)Copying Strings and Arrays.
* memrchr: (libc)Search Functions.
* memset: (libc)Copying Strings and Arrays.
* mkdir: (libc)Creating Directories.
* mkdtemp: (libc)Temporary Files.
* mkfifo: (libc)FIFO Special Files.
* mknod: (libc)Making Special Files.
* mkstemp: (libc)Temporary Files.
* mktemp: (libc)Temporary Files.
* mktime: (libc)Broken-down Time.
* mlock2: (libc)Page Lock Functions.
* mlock: (libc)Page Lock Functions.
* mlockall: (libc)Page Lock Functions.
* mmap64: (libc)Memory-mapped I/O.
* mmap: (libc)Memory-mapped I/O.
* modf: (libc)Rounding Functions.
* modff: (libc)Rounding Functions.
* modffN: (libc)Rounding Functions.
* modffNx: (libc)Rounding Functions.
* modfl: (libc)Rounding Functions.
* mount: (libc)Mount-Unmount-Remount.
* mprobe: (libc)Heap Consistency Checking.
* mprotect: (libc)Memory Protection.
* mrand48: (libc)SVID Random.
* mrand48_r: (libc)SVID Random.
* mremap: (libc)Memory-mapped I/O.
* msync: (libc)Memory-mapped I/O.
* mtrace: (libc)Tracing malloc.
* mtx_destroy: (libc)ISO C Mutexes.
* mtx_init: (libc)ISO C Mutexes.
* mtx_lock: (libc)ISO C Mutexes.
* mtx_timedlock: (libc)ISO C Mutexes.
* mtx_trylock: (libc)ISO C Mutexes.
* mtx_unlock: (libc)ISO C Mutexes.
* munlock: (libc)Page Lock Functions.
* munlockall: (libc)Page Lock Functions.
* munmap: (libc)Memory-mapped I/O.
* muntrace: (libc)Tracing malloc.
* nan: (libc)FP Bit Twiddling.
* nanf: (libc)FP Bit Twiddling.
* nanfN: (libc)FP Bit Twiddling.
* nanfNx: (libc)FP Bit Twiddling.
* nanl: (libc)FP Bit Twiddling.
* nanosleep: (libc)Sleeping.
* nearbyint: (libc)Rounding Functions.
* nearbyintf: (libc)Rounding Functions.
* nearbyintfN: (libc)Rounding Functions.
* nearbyintfNx: (libc)Rounding Functions.
* nearbyintl: (libc)Rounding Functions.
* nextafter: (libc)FP Bit Twiddling.
* nextafterf: (libc)FP Bit Twiddling.
* nextafterfN: (libc)FP Bit Twiddling.
* nextafterfNx: (libc)FP Bit Twiddling.
* nextafterl: (libc)FP Bit Twiddling.
* nextdown: (libc)FP Bit Twiddling.
* nextdownf: (libc)FP Bit Twiddling.
* nextdownfN: (libc)FP Bit Twiddling.
* nextdownfNx: (libc)FP Bit Twiddling.
* nextdownl: (libc)FP Bit Twiddling.
* nexttoward: (libc)FP Bit Twiddling.
* nexttowardf: (libc)FP Bit Twiddling.
* nexttowardl: (libc)FP Bit Twiddling.
* nextup: (libc)FP Bit Twiddling.
* nextupf: (libc)FP Bit Twiddling.
* nextupfN: (libc)FP Bit Twiddling.
* nextupfNx: (libc)FP Bit Twiddling.
* nextupl: (libc)FP Bit Twiddling.
* nftw64: (libc)Working with Directory Trees.
* nftw: (libc)Working with Directory Trees.
* ngettext: (libc)Advanced gettext functions.
* nice: (libc)Traditional Scheduling Functions.
* nl_langinfo: (libc)The Elegant and Fast Way.
* nrand48: (libc)SVID Random.
* nrand48_r: (libc)SVID Random.
* ntohl: (libc)Byte Order.
* ntohs: (libc)Byte Order.
* ntp_adjtime: (libc)High Accuracy Clock.
* ntp_gettime: (libc)High Accuracy Clock.
* obstack_1grow: (libc)Growing Objects.
* obstack_1grow_fast: (libc)Extra Fast Growing.
* obstack_alignment_mask: (libc)Obstacks Data Alignment.
* obstack_alloc: (libc)Allocation in an Obstack.
* obstack_base: (libc)Status of an Obstack.
* obstack_blank: (libc)Growing Objects.
* obstack_blank_fast: (libc)Extra Fast Growing.
* obstack_chunk_size: (libc)Obstack Chunks.
* obstack_copy0: (libc)Allocation in an Obstack.
* obstack_copy: (libc)Allocation in an Obstack.
* obstack_finish: (libc)Growing Objects.
* obstack_free: (libc)Freeing Obstack Objects.
* obstack_grow0: (libc)Growing Objects.
* obstack_grow: (libc)Growing Objects.
* obstack_init: (libc)Preparing for Obstacks.
* obstack_int_grow: (libc)Growing Objects.
* obstack_int_grow_fast: (libc)Extra Fast Growing.
* obstack_next_free: (libc)Status of an Obstack.
* obstack_object_size: (libc)Growing Objects.
* obstack_object_size: (libc)Status of an Obstack.
* obstack_printf: (libc)Dynamic Output.
* obstack_ptr_grow: (libc)Growing Objects.
* obstack_ptr_grow_fast: (libc)Extra Fast Growing.
* obstack_room: (libc)Extra Fast Growing.
* obstack_vprintf: (libc)Variable Arguments Output.
* offsetof: (libc)Structure Measurement.
* on_exit: (libc)Cleanups on Exit.
* open64: (libc)Opening and Closing Files.
* open: (libc)Opening and Closing Files.
* open_memstream: (libc)String Streams.
* opendir: (libc)Opening a Directory.
* openlog: (libc)openlog.
* openpty: (libc)Pseudo-Terminal Pairs.
* parse_printf_format: (libc)Parsing a Template String.
* pathconf: (libc)Pathconf.
* pause: (libc)Using Pause.
* pclose: (libc)Pipe to a Subprocess.
* perror: (libc)Error Messages.
* pipe: (libc)Creating a Pipe.
* pkey_alloc: (libc)Memory Protection.
* pkey_free: (libc)Memory Protection.
* pkey_get: (libc)Memory Protection.
* pkey_mprotect: (libc)Memory Protection.
* pkey_set: (libc)Memory Protection.
* popen: (libc)Pipe to a Subprocess.
* posix_fallocate64: (libc)Storage Allocation.
* posix_fallocate: (libc)Storage Allocation.
* posix_memalign: (libc)Aligned Memory Blocks.
* pow: (libc)Exponents and Logarithms.
* powf: (libc)Exponents and Logarithms.
* powfN: (libc)Exponents and Logarithms.
* powfNx: (libc)Exponents and Logarithms.
* powl: (libc)Exponents and Logarithms.
* pread64: (libc)I/O Primitives.
* pread: (libc)I/O Primitives.
* preadv2: (libc)Scatter-Gather.
* preadv64: (libc)Scatter-Gather.
* preadv64v2: (libc)Scatter-Gather.
* preadv: (libc)Scatter-Gather.
* printf: (libc)Formatted Output Functions.
* printf_size: (libc)Predefined Printf Handlers.
* printf_size_info: (libc)Predefined Printf Handlers.
* psignal: (libc)Signal Messages.
* pthread_cond_clockwait: (libc)Default Thread Attributes.
* pthread_getattr_default_np: (libc)Default Thread Attributes.
* pthread_getspecific: (libc)Thread-specific Data.
* pthread_key_create: (libc)Thread-specific Data.
* pthread_key_delete: (libc)Thread-specific Data.
* pthread_rwlock_clockrdlock: (libc)Default Thread Attributes.
* pthread_rwlock_clockwrlock: (libc)Default Thread Attributes.
* pthread_setattr_default_np: (libc)Default Thread Attributes.
* pthread_setspecific: (libc)Thread-specific Data.
* ptsname: (libc)Allocation.
* ptsname_r: (libc)Allocation.
* putc: (libc)Simple Output.
* putc_unlocked: (libc)Simple Output.
* putchar: (libc)Simple Output.
* putchar_unlocked: (libc)Simple Output.
* putenv: (libc)Environment Access.
* putpwent: (libc)Writing a User Entry.
* puts: (libc)Simple Output.
* pututline: (libc)Manipulating the Database.
* pututxline: (libc)XPG Functions.
* putw: (libc)Simple Output.
* putwc: (libc)Simple Output.
* putwc_unlocked: (libc)Simple Output.
* putwchar: (libc)Simple Output.
* putwchar_unlocked: (libc)Simple Output.
* pwrite64: (libc)I/O Primitives.
* pwrite: (libc)I/O Primitives.
* pwritev2: (libc)Scatter-Gather.
* pwritev64: (libc)Scatter-Gather.
* pwritev64v2: (libc)Scatter-Gather.
* pwritev: (libc)Scatter-Gather.
* qecvt: (libc)System V Number Conversion.
* qecvt_r: (libc)System V Number Conversion.
* qfcvt: (libc)System V Number Conversion.
* qfcvt_r: (libc)System V Number Conversion.
* qgcvt: (libc)System V Number Conversion.
* qsort: (libc)Array Sort Function.
* raise: (libc)Signaling Yourself.
* rand: (libc)ISO Random.
* rand_r: (libc)ISO Random.
* random: (libc)BSD Random.
* random_r: (libc)BSD Random.
* rawmemchr: (libc)Search Functions.
* read: (libc)I/O Primitives.
* readdir64: (libc)Reading/Closing Directory.
* readdir64_r: (libc)Reading/Closing Directory.
* readdir: (libc)Reading/Closing Directory.
* readdir_r: (libc)Reading/Closing Directory.
* readlink: (libc)Symbolic Links.
* readv: (libc)Scatter-Gather.
* realloc: (libc)Changing Block Size.
* reallocarray: (libc)Changing Block Size.
* realpath: (libc)Symbolic Links.
* recv: (libc)Receiving Data.
* recvfrom: (libc)Receiving Datagrams.
* recvmsg: (libc)Receiving Datagrams.
* regcomp: (libc)POSIX Regexp Compilation.
* regerror: (libc)Regexp Cleanup.
* regexec: (libc)Matching POSIX Regexps.
* regfree: (libc)Regexp Cleanup.
* register_printf_function: (libc)Registering New Conversions.
* remainder: (libc)Remainder Functions.
* remainderf: (libc)Remainder Functions.
* remainderfN: (libc)Remainder Functions.
* remainderfNx: (libc)Remainder Functions.
* remainderl: (libc)Remainder Functions.
* remove: (libc)Deleting Files.
* rename: (libc)Renaming Files.
* rewind: (libc)File Positioning.
* rewinddir: (libc)Random Access Directory.
* rindex: (libc)Search Functions.
* rint: (libc)Rounding Functions.
* rintf: (libc)Rounding Functions.
* rintfN: (libc)Rounding Functions.
* rintfNx: (libc)Rounding Functions.
* rintl: (libc)Rounding Functions.
* rmdir: (libc)Deleting Files.
* round: (libc)Rounding Functions.
* roundeven: (libc)Rounding Functions.
* roundevenf: (libc)Rounding Functions.
* roundevenfN: (libc)Rounding Functions.
* roundevenfNx: (libc)Rounding Functions.
* roundevenl: (libc)Rounding Functions.
* roundf: (libc)Rounding Functions.
* roundfN: (libc)Rounding Functions.
* roundfNx: (libc)Rounding Functions.
* roundl: (libc)Rounding Functions.
* rpmatch: (libc)Yes-or-No Questions.
* sbrk: (libc)Resizing the Data Segment.
* scalb: (libc)Normalization Functions.
* scalbf: (libc)Normalization Functions.
* scalbl: (libc)Normalization Functions.
* scalbln: (libc)Normalization Functions.
* scalblnf: (libc)Normalization Functions.
* scalblnfN: (libc)Normalization Functions.
* scalblnfNx: (libc)Normalization Functions.
* scalblnl: (libc)Normalization Functions.
* scalbn: (libc)Normalization Functions.
* scalbnf: (libc)Normalization Functions.
* scalbnfN: (libc)Normalization Functions.
* scalbnfNx: (libc)Normalization Functions.
* scalbnl: (libc)Normalization Functions.
* scandir64: (libc)Scanning Directory Content.
* scandir: (libc)Scanning Directory Content.
* scanf: (libc)Formatted Input Functions.
* sched_get_priority_max: (libc)Basic Scheduling Functions.
* sched_get_priority_min: (libc)Basic Scheduling Functions.
* sched_getaffinity: (libc)CPU Affinity.
* sched_getparam: (libc)Basic Scheduling Functions.
* sched_getscheduler: (libc)Basic Scheduling Functions.
* sched_rr_get_interval: (libc)Basic Scheduling Functions.
* sched_setaffinity: (libc)CPU Affinity.
* sched_setparam: (libc)Basic Scheduling Functions.
* sched_setscheduler: (libc)Basic Scheduling Functions.
* sched_yield: (libc)Basic Scheduling Functions.
* secure_getenv: (libc)Environment Access.
* seed48: (libc)SVID Random.
* seed48_r: (libc)SVID Random.
* seekdir: (libc)Random Access Directory.
* select: (libc)Waiting for I/O.
* sem_clockwait: (libc)Default Thread Attributes.
* sem_close: (libc)Semaphores.
* sem_destroy: (libc)Semaphores.
* sem_getvalue: (libc)Semaphores.
* sem_init: (libc)Semaphores.
* sem_open: (libc)Semaphores.
* sem_post: (libc)Semaphores.
* sem_timedwait: (libc)Semaphores.
* sem_trywait: (libc)Semaphores.
* sem_unlink: (libc)Semaphores.
* sem_wait: (libc)Semaphores.
* semctl: (libc)Semaphores.
* semget: (libc)Semaphores.
* semop: (libc)Semaphores.
* semtimedop: (libc)Semaphores.
* send: (libc)Sending Data.
* sendmsg: (libc)Receiving Datagrams.
* sendto: (libc)Sending Datagrams.
* setbuf: (libc)Controlling Buffering.
* setbuffer: (libc)Controlling Buffering.
* setcontext: (libc)System V contexts.
* setdomainname: (libc)Host Identification.
* setegid: (libc)Setting Groups.
* setenv: (libc)Environment Access.
* seteuid: (libc)Setting User ID.
* setfsent: (libc)fstab.
* setgid: (libc)Setting Groups.
* setgrent: (libc)Scanning All Groups.
* setgroups: (libc)Setting Groups.
* sethostent: (libc)Host Names.
* sethostid: (libc)Host Identification.
* sethostname: (libc)Host Identification.
* setitimer: (libc)Setting an Alarm.
* setjmp: (libc)Non-Local Details.
* setlinebuf: (libc)Controlling Buffering.
* setlocale: (libc)Setting the Locale.
* setlogmask: (libc)setlogmask.
* setmntent: (libc)mtab.
* setnetent: (libc)Networks Database.
* setnetgrent: (libc)Lookup Netgroup.
* setpayload: (libc)FP Bit Twiddling.
* setpayloadf: (libc)FP Bit Twiddling.
* setpayloadfN: (libc)FP Bit Twiddling.
* setpayloadfNx: (libc)FP Bit Twiddling.
* setpayloadl: (libc)FP Bit Twiddling.
* setpayloadsig: (libc)FP Bit Twiddling.
* setpayloadsigf: (libc)FP Bit Twiddling.
* setpayloadsigfN: (libc)FP Bit Twiddling.
* setpayloadsigfNx: (libc)FP Bit Twiddling.
* setpayloadsigl: (libc)FP Bit Twiddling.
* setpgid: (libc)Process Group Functions.
* setpgrp: (libc)Process Group Functions.
* setpriority: (libc)Traditional Scheduling Functions.
* setprotoent: (libc)Protocols Database.
* setpwent: (libc)Scanning All Users.
* setregid: (libc)Setting Groups.
* setreuid: (libc)Setting User ID.
* setrlimit64: (libc)Limits on Resources.
* setrlimit: (libc)Limits on Resources.
* setservent: (libc)Services Database.
* setsid: (libc)Process Group Functions.
* setsockopt: (libc)Socket Option Functions.
* setstate: (libc)BSD Random.
* setstate_r: (libc)BSD Random.
* settimeofday: (libc)High-Resolution Calendar.
* setuid: (libc)Setting User ID.
* setutent: (libc)Manipulating the Database.
* setutxent: (libc)XPG Functions.
* setvbuf: (libc)Controlling Buffering.
* shm_open: (libc)Memory-mapped I/O.
* shm_unlink: (libc)Memory-mapped I/O.
* shutdown: (libc)Closing a Socket.
* sigaction: (libc)Advanced Signal Handling.
* sigaddset: (libc)Signal Sets.
* sigaltstack: (libc)Signal Stack.
* sigblock: (libc)BSD Signal Handling.
* sigdelset: (libc)Signal Sets.
* sigemptyset: (libc)Signal Sets.
* sigfillset: (libc)Signal Sets.
* siginterrupt: (libc)BSD Signal Handling.
* sigismember: (libc)Signal Sets.
* siglongjmp: (libc)Non-Local Exits and Signals.
* sigmask: (libc)BSD Signal Handling.
* signal: (libc)Basic Signal Handling.
* signbit: (libc)FP Bit Twiddling.
* significand: (libc)Normalization Functions.
* significandf: (libc)Normalization Functions.
* significandl: (libc)Normalization Functions.
* sigpause: (libc)BSD Signal Handling.
* sigpending: (libc)Checking for Pending Signals.
* sigprocmask: (libc)Process Signal Mask.
* sigsetjmp: (libc)Non-Local Exits and Signals.
* sigsetmask: (libc)BSD Signal Handling.
* sigstack: (libc)Signal Stack.
* sigsuspend: (libc)Sigsuspend.
* sin: (libc)Trig Functions.
* sincos: (libc)Trig Functions.
* sincosf: (libc)Trig Functions.
* sincosfN: (libc)Trig Functions.
* sincosfNx: (libc)Trig Functions.
* sincosl: (libc)Trig Functions.
* sinf: (libc)Trig Functions.
* sinfN: (libc)Trig Functions.
* sinfNx: (libc)Trig Functions.
* sinh: (libc)Hyperbolic Functions.
* sinhf: (libc)Hyperbolic Functions.
* sinhfN: (libc)Hyperbolic Functions.
* sinhfNx: (libc)Hyperbolic Functions.
* sinhl: (libc)Hyperbolic Functions.
* sinl: (libc)Trig Functions.
* sleep: (libc)Sleeping.
* snprintf: (libc)Formatted Output Functions.
* socket: (libc)Creating a Socket.
* socketpair: (libc)Socket Pairs.
* sprintf: (libc)Formatted Output Functions.
* sqrt: (libc)Exponents and Logarithms.
* sqrtf: (libc)Exponents and Logarithms.
* sqrtfN: (libc)Exponents and Logarithms.
* sqrtfNx: (libc)Exponents and Logarithms.
* sqrtl: (libc)Exponents and Logarithms.
* srand48: (libc)SVID Random.
* srand48_r: (libc)SVID Random.
* srand: (libc)ISO Random.
* srandom: (libc)BSD Random.
* srandom_r: (libc)BSD Random.
* sscanf: (libc)Formatted Input Functions.
* ssignal: (libc)Basic Signal Handling.
* stat64: (libc)Reading Attributes.
* stat: (libc)Reading Attributes.
* stime: (libc)Simple Calendar Time.
* stpcpy: (libc)Copying Strings and Arrays.
* stpncpy: (libc)Truncating Strings.
* strcasecmp: (libc)String/Array Comparison.
* strcasestr: (libc)Search Functions.
* strcat: (libc)Concatenating Strings.
* strchr: (libc)Search Functions.
* strchrnul: (libc)Search Functions.
* strcmp: (libc)String/Array Comparison.
* strcoll: (libc)Collation Functions.
* strcpy: (libc)Copying Strings and Arrays.
* strcspn: (libc)Search Functions.
* strdup: (libc)Copying Strings and Arrays.
* strdupa: (libc)Copying Strings and Arrays.
* strerror: (libc)Error Messages.
* strerror_r: (libc)Error Messages.
* strfmon: (libc)Formatting Numbers.
* strfromd: (libc)Printing of Floats.
* strfromf: (libc)Printing of Floats.
* strfromfN: (libc)Printing of Floats.
* strfromfNx: (libc)Printing of Floats.
* strfroml: (libc)Printing of Floats.
* strfry: (libc)Shuffling Bytes.
* strftime: (libc)Formatting Calendar Time.
* strlen: (libc)String Length.
* strncasecmp: (libc)String/Array Comparison.
* strncat: (libc)Truncating Strings.
* strncmp: (libc)String/Array Comparison.
* strncpy: (libc)Truncating Strings.
* strndup: (libc)Truncating Strings.
* strndupa: (libc)Truncating Strings.
* strnlen: (libc)String Length.
* strpbrk: (libc)Search Functions.
* strptime: (libc)Low-Level Time String Parsing.
* strrchr: (libc)Search Functions.
* strsep: (libc)Finding Tokens in a String.
* strsignal: (libc)Signal Messages.
* strspn: (libc)Search Functions.
* strstr: (libc)Search Functions.
* strtod: (libc)Parsing of Floats.
* strtof: (libc)Parsing of Floats.
* strtofN: (libc)Parsing of Floats.
* strtofNx: (libc)Parsing of Floats.
* strtoimax: (libc)Parsing of Integers.
* strtok: (libc)Finding Tokens in a String.
* strtok_r: (libc)Finding Tokens in a String.
* strtol: (libc)Parsing of Integers.
* strtold: (libc)Parsing of Floats.
* strtoll: (libc)Parsing of Integers.
* strtoq: (libc)Parsing of Integers.
* strtoul: (libc)Parsing of Integers.
* strtoull: (libc)Parsing of Integers.
* strtoumax: (libc)Parsing of Integers.
* strtouq: (libc)Parsing of Integers.
* strverscmp: (libc)String/Array Comparison.
* strxfrm: (libc)Collation Functions.
* stty: (libc)BSD Terminal Modes.
* swapcontext: (libc)System V contexts.
* swprintf: (libc)Formatted Output Functions.
* swscanf: (libc)Formatted Input Functions.
* symlink: (libc)Symbolic Links.
* sync: (libc)Synchronizing I/O.
* syscall: (libc)System Calls.
* sysconf: (libc)Sysconf Definition.
* sysctl: (libc)System Parameters.
* syslog: (libc)syslog; vsyslog.
* system: (libc)Running a Command.
* sysv_signal: (libc)Basic Signal Handling.
* tan: (libc)Trig Functions.
* tanf: (libc)Trig Functions.
* tanfN: (libc)Trig Functions.
* tanfNx: (libc)Trig Functions.
* tanh: (libc)Hyperbolic Functions.
* tanhf: (libc)Hyperbolic Functions.
* tanhfN: (libc)Hyperbolic Functions.
* tanhfNx: (libc)Hyperbolic Functions.
* tanhl: (libc)Hyperbolic Functions.
* tanl: (libc)Trig Functions.
* tcdrain: (libc)Line Control.
* tcflow: (libc)Line Control.
* tcflush: (libc)Line Control.
* tcgetattr: (libc)Mode Functions.
* tcgetpgrp: (libc)Terminal Access Functions.
* tcgetsid: (libc)Terminal Access Functions.
* tcsendbreak: (libc)Line Control.
* tcsetattr: (libc)Mode Functions.
* tcsetpgrp: (libc)Terminal Access Functions.
* tdelete: (libc)Tree Search Function.
* tdestroy: (libc)Tree Search Function.
* telldir: (libc)Random Access Directory.
* tempnam: (libc)Temporary Files.
* textdomain: (libc)Locating gettext catalog.
* tfind: (libc)Tree Search Function.
* tgamma: (libc)Special Functions.
* tgammaf: (libc)Special Functions.
* tgammafN: (libc)Special Functions.
* tgammafNx: (libc)Special Functions.
* tgammal: (libc)Special Functions.
* tgkill: (libc)Signaling Another Process.
* thrd_create: (libc)ISO C Thread Management.
* thrd_current: (libc)ISO C Thread Management.
* thrd_detach: (libc)ISO C Thread Management.
* thrd_equal: (libc)ISO C Thread Management.
* thrd_exit: (libc)ISO C Thread Management.
* thrd_join: (libc)ISO C Thread Management.
* thrd_sleep: (libc)ISO C Thread Management.
* thrd_yield: (libc)ISO C Thread Management.
* time: (libc)Simple Calendar Time.
* timegm: (libc)Broken-down Time.
* timelocal: (libc)Broken-down Time.
* times: (libc)Processor Time.
* tmpfile64: (libc)Temporary Files.
* tmpfile: (libc)Temporary Files.
* tmpnam: (libc)Temporary Files.
* tmpnam_r: (libc)Temporary Files.
* toascii: (libc)Case Conversion.
* tolower: (libc)Case Conversion.
* totalorder: (libc)FP Comparison Functions.
* totalorderf: (libc)FP Comparison Functions.
* totalorderfN: (libc)FP Comparison Functions.
* totalorderfNx: (libc)FP Comparison Functions.
* totalorderl: (libc)FP Comparison Functions.
* totalordermag: (libc)FP Comparison Functions.
* totalordermagf: (libc)FP Comparison Functions.
* totalordermagfN: (libc)FP Comparison Functions.
* totalordermagfNx: (libc)FP Comparison Functions.
* totalordermagl: (libc)FP Comparison Functions.
* toupper: (libc)Case Conversion.
* towctrans: (libc)Wide Character Case Conversion.
* towlower: (libc)Wide Character Case Conversion.
* towupper: (libc)Wide Character Case Conversion.
* trunc: (libc)Rounding Functions.
* truncate64: (libc)File Size.
* truncate: (libc)File Size.
* truncf: (libc)Rounding Functions.
* truncfN: (libc)Rounding Functions.
* truncfNx: (libc)Rounding Functions.
* truncl: (libc)Rounding Functions.
* tsearch: (libc)Tree Search Function.
* tss_create: (libc)ISO C Thread-local Storage.
* tss_delete: (libc)ISO C Thread-local Storage.
* tss_get: (libc)ISO C Thread-local Storage.
* tss_set: (libc)ISO C Thread-local Storage.
* ttyname: (libc)Is It a Terminal.
* ttyname_r: (libc)Is It a Terminal.
* twalk: (libc)Tree Search Function.
* twalk_r: (libc)Tree Search Function.
* tzset: (libc)Time Zone Functions.
* ufromfp: (libc)Rounding Functions.
* ufromfpf: (libc)Rounding Functions.
* ufromfpfN: (libc)Rounding Functions.
* ufromfpfNx: (libc)Rounding Functions.
* ufromfpl: (libc)Rounding Functions.
* ufromfpx: (libc)Rounding Functions.
* ufromfpxf: (libc)Rounding Functions.
* ufromfpxfN: (libc)Rounding Functions.
* ufromfpxfNx: (libc)Rounding Functions.
* ufromfpxl: (libc)Rounding Functions.
* ulimit: (libc)Limits on Resources.
* umask: (libc)Setting Permissions.
* umount2: (libc)Mount-Unmount-Remount.
* umount: (libc)Mount-Unmount-Remount.
* uname: (libc)Platform Type.
* ungetc: (libc)How Unread.
* ungetwc: (libc)How Unread.
* unlink: (libc)Deleting Files.
* unlockpt: (libc)Allocation.
* unsetenv: (libc)Environment Access.
* updwtmp: (libc)Manipulating the Database.
* utime: (libc)File Times.
* utimes: (libc)File Times.
* utmpname: (libc)Manipulating the Database.
* utmpxname: (libc)XPG Functions.
* va_arg: (libc)Argument Macros.
* va_copy: (libc)Argument Macros.
* va_end: (libc)Argument Macros.
* va_start: (libc)Argument Macros.
* valloc: (libc)Aligned Memory Blocks.
* vasprintf: (libc)Variable Arguments Output.
* verr: (libc)Error Messages.
* verrx: (libc)Error Messages.
* versionsort64: (libc)Scanning Directory Content.
* versionsort: (libc)Scanning Directory Content.
* vfork: (libc)Creating a Process.
* vfprintf: (libc)Variable Arguments Output.
* vfscanf: (libc)Variable Arguments Input.
* vfwprintf: (libc)Variable Arguments Output.
* vfwscanf: (libc)Variable Arguments Input.
* vlimit: (libc)Limits on Resources.
* vprintf: (libc)Variable Arguments Output.
* vscanf: (libc)Variable Arguments Input.
* vsnprintf: (libc)Variable Arguments Output.
* vsprintf: (libc)Variable Arguments Output.
* vsscanf: (libc)Variable Arguments Input.
* vswprintf: (libc)Variable Arguments Output.
* vswscanf: (libc)Variable Arguments Input.
* vsyslog: (libc)syslog; vsyslog.
* vtimes: (libc)Resource Usage.
* vwarn: (libc)Error Messages.
* vwarnx: (libc)Error Messages.
* vwprintf: (libc)Variable Arguments Output.
* vwscanf: (libc)Variable Arguments Input.
* wait3: (libc)BSD Wait Functions.
* wait4: (libc)Process Completion.
* wait: (libc)Process Completion.
* waitpid: (libc)Process Completion.
* warn: (libc)Error Messages.
* warnx: (libc)Error Messages.
* wcpcpy: (libc)Copying Strings and Arrays.
* wcpncpy: (libc)Truncating Strings.
* wcrtomb: (libc)Converting a Character.
* wcscasecmp: (libc)String/Array Comparison.
* wcscat: (libc)Concatenating Strings.
* wcschr: (libc)Search Functions.
* wcschrnul: (libc)Search Functions.
* wcscmp: (libc)String/Array Comparison.
* wcscoll: (libc)Collation Functions.
* wcscpy: (libc)Copying Strings and Arrays.
* wcscspn: (libc)Search Functions.
* wcsdup: (libc)Copying Strings and Arrays.
* wcsftime: (libc)Formatting Calendar Time.
* wcslen: (libc)String Length.
* wcsncasecmp: (libc)String/Array Comparison.
* wcsncat: (libc)Truncating Strings.
* wcsncmp: (libc)String/Array Comparison.
* wcsncpy: (libc)Truncating Strings.
* wcsnlen: (libc)String Length.
* wcsnrtombs: (libc)Converting Strings.
* wcspbrk: (libc)Search Functions.
* wcsrchr: (libc)Search Functions.
* wcsrtombs: (libc)Converting Strings.
* wcsspn: (libc)Search Functions.
* wcsstr: (libc)Search Functions.
* wcstod: (libc)Parsing of Floats.
* wcstof: (libc)Parsing of Floats.
* wcstofN: (libc)Parsing of Floats.
* wcstofNx: (libc)Parsing of Floats.
* wcstoimax: (libc)Parsing of Integers.
* wcstok: (libc)Finding Tokens in a String.
* wcstol: (libc)Parsing of Integers.
* wcstold: (libc)Parsing of Floats.
* wcstoll: (libc)Parsing of Integers.
* wcstombs: (libc)Non-reentrant String Conversion.
* wcstoq: (libc)Parsing of Integers.
* wcstoul: (libc)Parsing of Integers.
* wcstoull: (libc)Parsing of Integers.
* wcstoumax: (libc)Parsing of Integers.
* wcstouq: (libc)Parsing of Integers.
* wcswcs: (libc)Search Functions.
* wcsxfrm: (libc)Collation Functions.
* wctob: (libc)Converting a Character.
* wctomb: (libc)Non-reentrant Character Conversion.
* wctrans: (libc)Wide Character Case Conversion.
* wctype: (libc)Classification of Wide Characters.
* wmemchr: (libc)Search Functions.
* wmemcmp: (libc)String/Array Comparison.
* wmemcpy: (libc)Copying Strings and Arrays.
* wmemmove: (libc)Copying Strings and Arrays.
* wmempcpy: (libc)Copying Strings and Arrays.
* wmemset: (libc)Copying Strings and Arrays.
* wordexp: (libc)Calling Wordexp.
* wordfree: (libc)Calling Wordexp.
* wprintf: (libc)Formatted Output Functions.
* write: (libc)I/O Primitives.
* writev: (libc)Scatter-Gather.
* wscanf: (libc)Formatted Input Functions.
* y0: (libc)Special Functions.
* y0f: (libc)Special Functions.
* y0fN: (libc)Special Functions.
* y0fNx: (libc)Special Functions.
* y0l: (libc)Special Functions.
* y1: (libc)Special Functions.
* y1f: (libc)Special Functions.
* y1fN: (libc)Special Functions.
* y1fNx: (libc)Special Functions.
* y1l: (libc)Special Functions.
* yn: (libc)Special Functions.
* ynf: (libc)Special Functions.
* ynfN: (libc)Special Functions.
* ynfNx: (libc)Special Functions.
* ynl: (libc)Special Functions.
END-INFO-DIR-ENTRY


File: libc.info,  Node: Setting Modes,  Next: Input Modes,  Prev: Mode Functions,  Up: Terminal Modes

17.4.3 Setting Terminal Modes Properly
--------------------------------------

When you set terminal modes, you should call ‘tcgetattr’ first to get
the current modes of the particular terminal device, modify only those
modes that you are really interested in, and store the result with
‘tcsetattr’.

   It’s a bad idea to simply initialize a ‘struct termios’ structure to
a chosen set of attributes and pass it directly to ‘tcsetattr’.  Your
program may be run years from now, on systems that support members not
documented in this manual.  The way to avoid setting these members to
unreasonable values is to avoid changing them.

   What’s more, different terminal devices may require different mode
settings in order to function properly.  So you should avoid blindly
copying attributes from one terminal device to another.

   When a member contains a collection of independent flags, as the
‘c_iflag’, ‘c_oflag’ and ‘c_cflag’ members do, even setting the entire
member is a bad idea, because particular operating systems have their
own flags.  Instead, you should start with the current value of the
member and alter only the flags whose values matter in your program,
leaving any other flags unchanged.

   Here is an example of how to set one flag (‘ISTRIP’) in the ‘struct
termios’ structure while properly preserving all the other data in the
structure:

     int
     set_istrip (int desc, int value)
     {
       struct termios settings;
       int result;

       result = tcgetattr (desc, &settings);
       if (result < 0)
         {
           perror ("error in tcgetattr");
           return 0;
         }
       settings.c_iflag &= ~ISTRIP;
       if (value)
         settings.c_iflag |= ISTRIP;
       result = tcsetattr (desc, TCSANOW, &settings);
       if (result < 0)
         {
           perror ("error in tcsetattr");
           return 0;
        }
       return 1;
     }


File: libc.info,  Node: Input Modes,  Next: Output Modes,  Prev: Setting Modes,  Up: Terminal Modes

17.4.4 Input Modes
------------------

This section describes the terminal attribute flags that control fairly
low-level aspects of input processing: handling of parity errors, break
signals, flow control, and <RET> and <LFD> characters.

   All of these flags are bits in the ‘c_iflag’ member of the ‘struct
termios’ structure.  The member is an integer, and you change flags
using the operators ‘&’, ‘|’ and ‘^’.  Don’t try to specify the entire
value for ‘c_iflag’—instead, change only specific flags and leave the
rest untouched (*note Setting Modes::).

 -- Macro: tcflag_t INPCK

     If this bit is set, input parity checking is enabled.  If it is not
     set, no checking at all is done for parity errors on input; the
     characters are simply passed through to the application.

     Parity checking on input processing is independent of whether
     parity detection and generation on the underlying terminal hardware
     is enabled; see *note Control Modes::.  For example, you could
     clear the ‘INPCK’ input mode flag and set the ‘PARENB’ control mode
     flag to ignore parity errors on input, but still generate parity on
     output.

     If this bit is set, what happens when a parity error is detected
     depends on whether the ‘IGNPAR’ or ‘PARMRK’ bits are set.  If
     neither of these bits are set, a byte with a parity error is passed
     to the application as a ‘'\0'’ character.

 -- Macro: tcflag_t IGNPAR

     If this bit is set, any byte with a framing or parity error is
     ignored.  This is only useful if ‘INPCK’ is also set.

 -- Macro: tcflag_t PARMRK

     If this bit is set, input bytes with parity or framing errors are
     marked when passed to the program.  This bit is meaningful only
     when ‘INPCK’ is set and ‘IGNPAR’ is not set.

     The way erroneous bytes are marked is with two preceding bytes,
     ‘377’ and ‘0’.  Thus, the program actually reads three bytes for
     one erroneous byte received from the terminal.

     If a valid byte has the value ‘0377’, and ‘ISTRIP’ (see below) is
     not set, the program might confuse it with the prefix that marks a
     parity error.  So a valid byte ‘0377’ is passed to the program as
     two bytes, ‘0377’ ‘0377’, in this case.

 -- Macro: tcflag_t ISTRIP

     If this bit is set, valid input bytes are stripped to seven bits;
     otherwise, all eight bits are available for programs to read.

 -- Macro: tcflag_t IGNBRK

     If this bit is set, break conditions are ignored.

     A "break condition" is defined in the context of asynchronous
     serial data transmission as a series of zero-value bits longer than
     a single byte.

 -- Macro: tcflag_t BRKINT

     If this bit is set and ‘IGNBRK’ is not set, a break condition
     clears the terminal input and output queues and raises a ‘SIGINT’
     signal for the foreground process group associated with the
     terminal.

     If neither ‘BRKINT’ nor ‘IGNBRK’ are set, a break condition is
     passed to the application as a single ‘'\0'’ character if ‘PARMRK’
     is not set, or otherwise as a three-character sequence ‘'\377'’,
     ‘'\0'’, ‘'\0'’.

 -- Macro: tcflag_t IGNCR

     If this bit is set, carriage return characters (‘'\r'’) are
     discarded on input.  Discarding carriage return may be useful on
     terminals that send both carriage return and linefeed when you type
     the <RET> key.

 -- Macro: tcflag_t ICRNL

     If this bit is set and ‘IGNCR’ is not set, carriage return
     characters (‘'\r'’) received as input are passed to the application
     as newline characters (‘'\n'’).

 -- Macro: tcflag_t INLCR

     If this bit is set, newline characters (‘'\n'’) received as input
     are passed to the application as carriage return characters
     (‘'\r'’).

 -- Macro: tcflag_t IXOFF

     If this bit is set, start/stop control on input is enabled.  In
     other words, the computer sends STOP and START characters as
     necessary to prevent input from coming in faster than programs are
     reading it.  The idea is that the actual terminal hardware that is
     generating the input data responds to a STOP character by
     suspending transmission, and to a START character by resuming
     transmission.  *Note Start/Stop Characters::.

 -- Macro: tcflag_t IXON

     If this bit is set, start/stop control on output is enabled.  In
     other words, if the computer receives a STOP character, it suspends
     output until a START character is received.  In this case, the STOP
     and START characters are never passed to the application program.
     If this bit is not set, then START and STOP can be read as ordinary
     characters.  *Note Start/Stop Characters::.

 -- Macro: tcflag_t IXANY

     If this bit is set, any input character restarts output when output
     has been suspended with the STOP character.  Otherwise, only the
     START character restarts output.

     This is a BSD extension; it exists only on BSD systems and
     GNU/Linux and GNU/Hurd systems.

 -- Macro: tcflag_t IMAXBEL

     If this bit is set, then filling up the terminal input buffer sends
     a BEL character (code ‘007’) to the terminal to ring the bell.

     This is a BSD extension.


File: libc.info,  Node: Output Modes,  Next: Control Modes,  Prev: Input Modes,  Up: Terminal Modes

17.4.5 Output Modes
-------------------

This section describes the terminal flags and fields that control how
output characters are translated and padded for display.  All of these
are contained in the ‘c_oflag’ member of the ‘struct termios’ structure.

   The ‘c_oflag’ member itself is an integer, and you change the flags
and fields using the operators ‘&’, ‘|’, and ‘^’.  Don’t try to specify
the entire value for ‘c_oflag’—instead, change only specific flags and
leave the rest untouched (*note Setting Modes::).

 -- Macro: tcflag_t OPOST

     If this bit is set, output data is processed in some unspecified
     way so that it is displayed appropriately on the terminal device.
     This typically includes mapping newline characters (‘'\n'’) onto
     carriage return and linefeed pairs.

     If this bit isn’t set, the characters are transmitted as-is.

   The following three bits are effective only if ‘OPOST’ is set.

 -- Macro: tcflag_t ONLCR

     If this bit is set, convert the newline character on output into a
     pair of characters, carriage return followed by linefeed.

 -- Macro: tcflag_t OXTABS

     If this bit is set, convert tab characters on output into the
     appropriate number of spaces to emulate a tab stop every eight
     columns.  This bit exists only on BSD systems and GNU/Hurd systems;
     on GNU/Linux systems it is available as ‘XTABS’.

 -- Macro: tcflag_t ONOEOT

     If this bit is set, discard ‘C-d’ characters (code ‘004’) on
     output.  These characters cause many dial-up terminals to
     disconnect.  This bit exists only on BSD systems and GNU/Hurd
     systems.


File: libc.info,  Node: Control Modes,  Next: Local Modes,  Prev: Output Modes,  Up: Terminal Modes

17.4.6 Control Modes
--------------------

This section describes the terminal flags and fields that control
parameters usually associated with asynchronous serial data
transmission.  These flags may not make sense for other kinds of
terminal ports (such as a network connection pseudo-terminal).  All of
these are contained in the ‘c_cflag’ member of the ‘struct termios’
structure.

   The ‘c_cflag’ member itself is an integer, and you change the flags
and fields using the operators ‘&’, ‘|’, and ‘^’.  Don’t try to specify
the entire value for ‘c_cflag’—instead, change only specific flags and
leave the rest untouched (*note Setting Modes::).

 -- Macro: tcflag_t CLOCAL

     If this bit is set, it indicates that the terminal is connected
     “locally” and that the modem status lines (such as carrier detect)
     should be ignored.

     On many systems if this bit is not set and you call ‘open’ without
     the ‘O_NONBLOCK’ flag set, ‘open’ blocks until a modem connection
     is established.

     If this bit is not set and a modem disconnect is detected, a
     ‘SIGHUP’ signal is sent to the controlling process group for the
     terminal (if it has one).  Normally, this causes the process to
     exit; see *note Signal Handling::.  Reading from the terminal after
     a disconnect causes an end-of-file condition, and writing causes an
     ‘EIO’ error to be returned.  The terminal device must be closed and
     reopened to clear the condition.

 -- Macro: tcflag_t HUPCL

     If this bit is set, a modem disconnect is generated when all
     processes that have the terminal device open have either closed the
     file or exited.

 -- Macro: tcflag_t CREAD

     If this bit is set, input can be read from the terminal.
     Otherwise, input is discarded when it arrives.

 -- Macro: tcflag_t CSTOPB

     If this bit is set, two stop bits are used.  Otherwise, only one
     stop bit is used.

 -- Macro: tcflag_t PARENB

     If this bit is set, generation and detection of a parity bit are
     enabled.  *Note Input Modes::, for information on how input parity
     errors are handled.

     If this bit is not set, no parity bit is added to output
     characters, and input characters are not checked for correct
     parity.

 -- Macro: tcflag_t PARODD

     This bit is only useful if ‘PARENB’ is set.  If ‘PARODD’ is set,
     odd parity is used, otherwise even parity is used.

   The control mode flags also includes a field for the number of bits
per character.  You can use the ‘CSIZE’ macro as a mask to extract the
value, like this: ‘settings.c_cflag & CSIZE’.

 -- Macro: tcflag_t CSIZE

     This is a mask for the number of bits per character.

 -- Macro: tcflag_t CS5

     This specifies five bits per byte.

 -- Macro: tcflag_t CS6

     This specifies six bits per byte.

 -- Macro: tcflag_t CS7

     This specifies seven bits per byte.

 -- Macro: tcflag_t CS8

     This specifies eight bits per byte.

   The following four bits are BSD extensions; these exist only on BSD
systems and GNU/Hurd systems.

 -- Macro: tcflag_t CCTS_OFLOW

     If this bit is set, enable flow control of output based on the CTS
     wire (RS232 protocol).

 -- Macro: tcflag_t CRTS_IFLOW

     If this bit is set, enable flow control of input based on the RTS
     wire (RS232 protocol).

 -- Macro: tcflag_t MDMBUF

     If this bit is set, enable carrier-based flow control of output.

 -- Macro: tcflag_t CIGNORE

     If this bit is set, it says to ignore the control modes and line
     speed values entirely.  This is only meaningful in a call to
     ‘tcsetattr’.

     The ‘c_cflag’ member and the line speed values returned by
     ‘cfgetispeed’ and ‘cfgetospeed’ will be unaffected by the call.
     ‘CIGNORE’ is useful if you want to set all the software modes in
     the other members, but leave the hardware details in ‘c_cflag’
     unchanged.  (This is how the ‘TCSASOFT’ flag to ‘tcsettattr’
     works.)

     This bit is never set in the structure filled in by ‘tcgetattr’.


File: libc.info,  Node: Local Modes,  Next: Line Speed,  Prev: Control Modes,  Up: Terminal Modes

17.4.7 Local Modes
------------------

This section describes the flags for the ‘c_lflag’ member of the ‘struct
termios’ structure.  These flags generally control higher-level aspects
of input processing than the input modes flags described in *note Input
Modes::, such as echoing, signals, and the choice of canonical or
noncanonical input.

   The ‘c_lflag’ member itself is an integer, and you change the flags
and fields using the operators ‘&’, ‘|’, and ‘^’.  Don’t try to specify
the entire value for ‘c_lflag’—instead, change only specific flags and
leave the rest untouched (*note Setting Modes::).

 -- Macro: tcflag_t ICANON

     This bit, if set, enables canonical input processing mode.
     Otherwise, input is processed in noncanonical mode.  *Note
     Canonical or Not::.

 -- Macro: tcflag_t ECHO

     If this bit is set, echoing of input characters back to the
     terminal is enabled.

 -- Macro: tcflag_t ECHOE

     If this bit is set, echoing indicates erasure of input with the
     ERASE character by erasing the last character in the current line
     from the screen.  Otherwise, the character erased is re-echoed to
     show what has happened (suitable for a printing terminal).

     This bit only controls the display behavior; the ‘ICANON’ bit by
     itself controls actual recognition of the ERASE character and
     erasure of input, without which ‘ECHOE’ is simply irrelevant.

 -- Macro: tcflag_t ECHOPRT

     This bit, like ‘ECHOE’, enables display of the ERASE character in a
     way that is geared to a hardcopy terminal.  When you type the ERASE
     character, a ‘\’ character is printed followed by the first
     character erased.  Typing the ERASE character again just prints the
     next character erased.  Then, the next time you type a normal
     character, a ‘/’ character is printed before the character echoes.

     This is a BSD extension, and exists only in BSD systems and
     GNU/Linux and GNU/Hurd systems.

 -- Macro: tcflag_t ECHOK

     This bit enables special display of the KILL character by moving to
     a new line after echoing the KILL character normally.  The behavior
     of ‘ECHOKE’ (below) is nicer to look at.

     If this bit is not set, the KILL character echoes just as it would
     if it were not the KILL character.  Then it is up to the user to
     remember that the KILL character has erased the preceding input;
     there is no indication of this on the screen.

     This bit only controls the display behavior; the ‘ICANON’ bit by
     itself controls actual recognition of the KILL character and
     erasure of input, without which ‘ECHOK’ is simply irrelevant.

 -- Macro: tcflag_t ECHOKE

     This bit is similar to ‘ECHOK’.  It enables special display of the
     KILL character by erasing on the screen the entire line that has
     been killed.  This is a BSD extension, and exists only in BSD
     systems and GNU/Linux and GNU/Hurd systems.

 -- Macro: tcflag_t ECHONL

     If this bit is set and the ‘ICANON’ bit is also set, then the
     newline (‘'\n'’) character is echoed even if the ‘ECHO’ bit is not
     set.

 -- Macro: tcflag_t ECHOCTL

     If this bit is set and the ‘ECHO’ bit is also set, echo control
     characters with ‘^’ followed by the corresponding text character.
     Thus, control-A echoes as ‘^A’.  This is usually the preferred mode
     for interactive input, because echoing a control character back to
     the terminal could have some undesired effect on the terminal.

     This is a BSD extension, and exists only in BSD systems and
     GNU/Linux and GNU/Hurd systems.

 -- Macro: tcflag_t ISIG

     This bit controls whether the INTR, QUIT, and SUSP characters are
     recognized.  The functions associated with these characters are
     performed if and only if this bit is set.  Being in canonical or
     noncanonical input mode has no effect on the interpretation of
     these characters.

     You should use caution when disabling recognition of these
     characters.  Programs that cannot be interrupted interactively are
     very user-unfriendly.  If you clear this bit, your program should
     provide some alternate interface that allows the user to
     interactively send the signals associated with these characters, or
     to escape from the program.

     *Note Signal Characters::.

 -- Macro: tcflag_t IEXTEN

     POSIX.1 gives ‘IEXTEN’ implementation-defined meaning, so you
     cannot rely on this interpretation on all systems.

     On BSD systems and GNU/Linux and GNU/Hurd systems, it enables the
     LNEXT and DISCARD characters.  *Note Other Special::.

 -- Macro: tcflag_t NOFLSH

     Normally, the INTR, QUIT, and SUSP characters cause input and
     output queues for the terminal to be cleared.  If this bit is set,
     the queues are not cleared.

 -- Macro: tcflag_t TOSTOP

     If this bit is set and the system supports job control, then
     ‘SIGTTOU’ signals are generated by background processes that
     attempt to write to the terminal.  *Note Access to the Terminal::.

   The following bits are BSD extensions; they exist only on BSD systems
and GNU/Hurd systems.

 -- Macro: tcflag_t ALTWERASE

     This bit determines how far the WERASE character should erase.  The
     WERASE character erases back to the beginning of a word; the
     question is, where do words begin?

     If this bit is clear, then the beginning of a word is a
     nonwhitespace character following a whitespace character.  If the
     bit is set, then the beginning of a word is an alphanumeric
     character or underscore following a character which is none of
     those.

     *Note Editing Characters::, for more information about the WERASE
     character.

 -- Macro: tcflag_t FLUSHO

     This is the bit that toggles when the user types the DISCARD
     character.  While this bit is set, all output is discarded.  *Note
     Other Special::.

 -- Macro: tcflag_t NOKERNINFO

     Setting this bit disables handling of the STATUS character.  *Note
     Other Special::.

 -- Macro: tcflag_t PENDIN

     If this bit is set, it indicates that there is a line of input that
     needs to be reprinted.  Typing the REPRINT character sets this bit;
     the bit remains set until reprinting is finished.  *Note Editing
     Characters::.


File: libc.info,  Node: Line Speed,  Next: Special Characters,  Prev: Local Modes,  Up: Terminal Modes

17.4.8 Line Speed
-----------------

The terminal line speed tells the computer how fast to read and write
data on the terminal.

   If the terminal is connected to a real serial line, the terminal
speed you specify actually controls the line—if it doesn’t match the
terminal’s own idea of the speed, communication does not work.  Real
serial ports accept only certain standard speeds.  Also, particular
hardware may not support even all the standard speeds.  Specifying a
speed of zero hangs up a dialup connection and turns off modem control
signals.

   If the terminal is not a real serial line (for example, if it is a
network connection), then the line speed won’t really affect data
transmission speed, but some programs will use it to determine the
amount of padding needed.  It’s best to specify a line speed value that
matches the actual speed of the actual terminal, but you can safely
experiment with different values to vary the amount of padding.

   There are actually two line speeds for each terminal, one for input
and one for output.  You can set them independently, but most often
terminals use the same speed for both directions.

   The speed values are stored in the ‘struct termios’ structure, but
don’t try to access them in the ‘struct termios’ structure directly.
Instead, you should use the following functions to read and store them:

 -- Function: speed_t cfgetospeed (const struct termios *TERMIOS-P)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function returns the output line speed stored in the structure
     ‘*TERMIOS-P’.

 -- Function: speed_t cfgetispeed (const struct termios *TERMIOS-P)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function returns the input line speed stored in the structure
     ‘*TERMIOS-P’.

 -- Function: int cfsetospeed (struct termios *TERMIOS-P, speed_t SPEED)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function stores SPEED in ‘*TERMIOS-P’ as the output speed.
     The normal return value is 0; a value of -1 indicates an error.  If
     SPEED is not a speed, ‘cfsetospeed’ returns -1.

 -- Function: int cfsetispeed (struct termios *TERMIOS-P, speed_t SPEED)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function stores SPEED in ‘*TERMIOS-P’ as the input speed.  The
     normal return value is 0; a value of -1 indicates an error.  If
     SPEED is not a speed, ‘cfsetospeed’ returns -1.

 -- Function: int cfsetspeed (struct termios *TERMIOS-P, speed_t SPEED)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function stores SPEED in ‘*TERMIOS-P’ as both the input and
     output speeds.  The normal return value is 0; a value of -1
     indicates an error.  If SPEED is not a speed, ‘cfsetspeed’ returns
     -1.  This function is an extension in 4.4 BSD.

 -- Data Type: speed_t

     The ‘speed_t’ type is an unsigned integer data type used to
     represent line speeds.

   The functions ‘cfsetospeed’ and ‘cfsetispeed’ report errors only for
speed values that the system simply cannot handle.  If you specify a
speed value that is basically acceptable, then those functions will
succeed.  But they do not check that a particular hardware device can
actually support the specified speeds—in fact, they don’t know which
device you plan to set the speed for.  If you use ‘tcsetattr’ to set the
speed of a particular device to a value that it cannot handle,
‘tcsetattr’ returns -1.

   *Portability note:* In the GNU C Library, the functions above accept
speeds measured in bits per second as input, and return speed values
measured in bits per second.  Other libraries require speeds to be
indicated by special codes.  For POSIX.1 portability, you must use one
of the following symbols to represent the speed; their precise numeric
values are system-dependent, but each name has a fixed meaning: ‘B110’
stands for 110 bps, ‘B300’ for 300 bps, and so on.  There is no portable
way to represent any speed but these, but these are the only speeds that
typical serial lines can support.

     B0  B50  B75  B110  B134  B150  B200
     B300  B600  B1200  B1800  B2400  B4800
     B9600  B19200  B38400  B57600  B115200
     B230400  B460800

   BSD defines two additional speed symbols as aliases: ‘EXTA’ is an
alias for ‘B19200’ and ‘EXTB’ is an alias for ‘B38400’.  These aliases
are obsolete.


File: libc.info,  Node: Special Characters,  Next: Noncanonical Input,  Prev: Line Speed,  Up: Terminal Modes

17.4.9 Special Characters
-------------------------

In canonical input, the terminal driver recognizes a number of special
characters which perform various control functions.  These include the
ERASE character (usually <DEL>) for editing input, and other editing
characters.  The INTR character (normally ‘C-c’) for sending a ‘SIGINT’
signal, and other signal-raising characters, may be available in either
canonical or noncanonical input mode.  All these characters are
described in this section.

   The particular characters used are specified in the ‘c_cc’ member of
the ‘struct termios’ structure.  This member is an array; each element
specifies the character for a particular role.  Each element has a
symbolic constant that stands for the index of that element—for example,
‘VINTR’ is the index of the element that specifies the INTR character,
so storing ‘'='’ in ‘TERMIOS.c_cc[VINTR]’ specifies ‘=’ as the INTR
character.

   On some systems, you can disable a particular special character
function by specifying the value ‘_POSIX_VDISABLE’ for that role.  This
value is unequal to any possible character code.  *Note Options for
Files::, for more information about how to tell whether the operating
system you are using supports ‘_POSIX_VDISABLE’.

* Menu:

* Editing Characters::          Special characters that terminate lines and
                                  delete text, and other editing functions.
* Signal Characters::           Special characters that send or raise signals
                                  to or for certain classes of processes.
* Start/Stop Characters::       Special characters that suspend or resume
                                  suspended output.
* Other Special::		Other special characters for BSD systems:
				  they can discard output, and print status.


File: libc.info,  Node: Editing Characters,  Next: Signal Characters,  Up: Special Characters

17.4.9.1 Characters for Input Editing
.....................................

These special characters are active only in canonical input mode.  *Note
Canonical or Not::.

 -- Macro: int VEOF

     This is the subscript for the EOF character in the special control
     character array.  ‘TERMIOS.c_cc[VEOF]’ holds the character itself.

     The EOF character is recognized only in canonical input mode.  It
     acts as a line terminator in the same way as a newline character,
     but if the EOF character is typed at the beginning of a line it
     causes ‘read’ to return a byte count of zero, indicating
     end-of-file.  The EOF character itself is discarded.

     Usually, the EOF character is ‘C-d’.

 -- Macro: int VEOL

     This is the subscript for the EOL character in the special control
     character array.  ‘TERMIOS.c_cc[VEOL]’ holds the character itself.

     The EOL character is recognized only in canonical input mode.  It
     acts as a line terminator, just like a newline character.  The EOL
     character is not discarded; it is read as the last character in the
     input line.

     You don’t need to use the EOL character to make <RET> end a line.
     Just set the ICRNL flag.  In fact, this is the default state of
     affairs.

 -- Macro: int VEOL2

     This is the subscript for the EOL2 character in the special control
     character array.  ‘TERMIOS.c_cc[VEOL2]’ holds the character itself.

     The EOL2 character works just like the EOL character (see above),
     but it can be a different character.  Thus, you can specify two
     characters to terminate an input line, by setting EOL to one of
     them and EOL2 to the other.

     The EOL2 character is a BSD extension; it exists only on BSD
     systems and GNU/Linux and GNU/Hurd systems.

 -- Macro: int VERASE

     This is the subscript for the ERASE character in the special
     control character array.  ‘TERMIOS.c_cc[VERASE]’ holds the
     character itself.

     The ERASE character is recognized only in canonical input mode.
     When the user types the erase character, the previous character
     typed is discarded.  (If the terminal generates multibyte character
     sequences, this may cause more than one byte of input to be
     discarded.)  This cannot be used to erase past the beginning of the
     current line of text.  The ERASE character itself is discarded.

     Usually, the ERASE character is <DEL>.

 -- Macro: int VWERASE

     This is the subscript for the WERASE character in the special
     control character array.  ‘TERMIOS.c_cc[VWERASE]’ holds the
     character itself.

     The WERASE character is recognized only in canonical mode.  It
     erases an entire word of prior input, and any whitespace after it;
     whitespace characters before the word are not erased.

     The definition of a “word” depends on the setting of the
     ‘ALTWERASE’ mode; *note Local Modes::.

     If the ‘ALTWERASE’ mode is not set, a word is defined as a sequence
     of any characters except space or tab.

     If the ‘ALTWERASE’ mode is set, a word is defined as a sequence of
     characters containing only letters, numbers, and underscores,
     optionally followed by one character that is not a letter, number,
     or underscore.

     The WERASE character is usually ‘C-w’.

     This is a BSD extension.

 -- Macro: int VKILL

     This is the subscript for the KILL character in the special control
     character array.  ‘TERMIOS.c_cc[VKILL]’ holds the character itself.

     The KILL character is recognized only in canonical input mode.
     When the user types the kill character, the entire contents of the
     current line of input are discarded.  The kill character itself is
     discarded too.

     The KILL character is usually ‘C-u’.

 -- Macro: int VREPRINT

     This is the subscript for the REPRINT character in the special
     control character array.  ‘TERMIOS.c_cc[VREPRINT]’ holds the
     character itself.

     The REPRINT character is recognized only in canonical mode.  It
     reprints the current input line.  If some asynchronous output has
     come while you are typing, this lets you see the line you are
     typing clearly again.

     The REPRINT character is usually ‘C-r’.

     This is a BSD extension.


File: libc.info,  Node: Signal Characters,  Next: Start/Stop Characters,  Prev: Editing Characters,  Up: Special Characters

17.4.9.2 Characters that Cause Signals
......................................

These special characters may be active in either canonical or
noncanonical input mode, but only when the ‘ISIG’ flag is set (*note
Local Modes::).

 -- Macro: int VINTR

     This is the subscript for the INTR character in the special control
     character array.  ‘TERMIOS.c_cc[VINTR]’ holds the character itself.

     The INTR (interrupt) character raises a ‘SIGINT’ signal for all
     processes in the foreground job associated with the terminal.  The
     INTR character itself is then discarded.  *Note Signal Handling::,
     for more information about signals.

     Typically, the INTR character is ‘C-c’.

 -- Macro: int VQUIT

     This is the subscript for the QUIT character in the special control
     character array.  ‘TERMIOS.c_cc[VQUIT]’ holds the character itself.

     The QUIT character raises a ‘SIGQUIT’ signal for all processes in
     the foreground job associated with the terminal.  The QUIT
     character itself is then discarded.  *Note Signal Handling::, for
     more information about signals.

     Typically, the QUIT character is ‘C-\’.

 -- Macro: int VSUSP

     This is the subscript for the SUSP character in the special control
     character array.  ‘TERMIOS.c_cc[VSUSP]’ holds the character itself.

     The SUSP (suspend) character is recognized only if the
     implementation supports job control (*note Job Control::).  It
     causes a ‘SIGTSTP’ signal to be sent to all processes in the
     foreground job associated with the terminal.  The SUSP character
     itself is then discarded.  *Note Signal Handling::, for more
     information about signals.

     Typically, the SUSP character is ‘C-z’.

   Few applications disable the normal interpretation of the SUSP
character.  If your program does this, it should provide some other
mechanism for the user to stop the job.  When the user invokes this
mechanism, the program should send a ‘SIGTSTP’ signal to the process
group of the process, not just to the process itself.  *Note Signaling
Another Process::.

 -- Macro: int VDSUSP

     This is the subscript for the DSUSP character in the special
     control character array.  ‘TERMIOS.c_cc[VDSUSP]’ holds the
     character itself.

     The DSUSP (suspend) character is recognized only if the
     implementation supports job control (*note Job Control::).  It
     sends a ‘SIGTSTP’ signal, like the SUSP character, but not right
     away—only when the program tries to read it as input.  Not all
     systems with job control support DSUSP; only BSD-compatible systems
     do (including GNU/Hurd systems).

     *Note Signal Handling::, for more information about signals.

     Typically, the DSUSP character is ‘C-y’.


File: libc.info,  Node: Start/Stop Characters,  Next: Other Special,  Prev: Signal Characters,  Up: Special Characters

17.4.9.3 Special Characters for Flow Control
............................................

These special characters may be active in either canonical or
noncanonical input mode, but their use is controlled by the flags ‘IXON’
and ‘IXOFF’ (*note Input Modes::).

 -- Macro: int VSTART

     This is the subscript for the START character in the special
     control character array.  ‘TERMIOS.c_cc[VSTART]’ holds the
     character itself.

     The START character is used to support the ‘IXON’ and ‘IXOFF’ input
     modes.  If ‘IXON’ is set, receiving a START character resumes
     suspended output; the START character itself is discarded.  If
     ‘IXANY’ is set, receiving any character at all resumes suspended
     output; the resuming character is not discarded unless it is the
     START character.  If ‘IXOFF’ is set, the system may also transmit
     START characters to the terminal.

     The usual value for the START character is ‘C-q’.  You may not be
     able to change this value—the hardware may insist on using ‘C-q’
     regardless of what you specify.

 -- Macro: int VSTOP

     This is the subscript for the STOP character in the special control
     character array.  ‘TERMIOS.c_cc[VSTOP]’ holds the character itself.

     The STOP character is used to support the ‘IXON’ and ‘IXOFF’ input
     modes.  If ‘IXON’ is set, receiving a STOP character causes output
     to be suspended; the STOP character itself is discarded.  If
     ‘IXOFF’ is set, the system may also transmit STOP characters to the
     terminal, to prevent the input queue from overflowing.

     The usual value for the STOP character is ‘C-s’.  You may not be
     able to change this value—the hardware may insist on using ‘C-s’
     regardless of what you specify.


File: libc.info,  Node: Other Special,  Prev: Start/Stop Characters,  Up: Special Characters

17.4.9.4 Other Special Characters
.................................

 -- Macro: int VLNEXT

     This is the subscript for the LNEXT character in the special
     control character array.  ‘TERMIOS.c_cc[VLNEXT]’ holds the
     character itself.

     The LNEXT character is recognized only when ‘IEXTEN’ is set, but in
     both canonical and noncanonical mode.  It disables any special
     significance of the next character the user types.  Even if the
     character would normally perform some editing function or generate
     a signal, it is read as a plain character.  This is the analogue of
     the ‘C-q’ command in Emacs.  “LNEXT” stands for “literal next.”

     The LNEXT character is usually ‘C-v’.

     This character is available on BSD systems and GNU/Linux and
     GNU/Hurd systems.

 -- Macro: int VDISCARD

     This is the subscript for the DISCARD character in the special
     control character array.  ‘TERMIOS.c_cc[VDISCARD]’ holds the
     character itself.

     The DISCARD character is recognized only when ‘IEXTEN’ is set, but
     in both canonical and noncanonical mode.  Its effect is to toggle
     the discard-output flag.  When this flag is set, all program output
     is discarded.  Setting the flag also discards all output currently
     in the output buffer.  Typing any other character resets the flag.

     This character is available on BSD systems and GNU/Linux and
     GNU/Hurd systems.

 -- Macro: int VSTATUS

     This is the subscript for the STATUS character in the special
     control character array.  ‘TERMIOS.c_cc[VSTATUS]’ holds the
     character itself.

     The STATUS character’s effect is to print out a status message
     about how the current process is running.

     The STATUS character is recognized only in canonical mode, and only
     if ‘NOKERNINFO’ is not set.

     This character is available only on BSD systems and GNU/Hurd
     systems.


File: libc.info,  Node: Noncanonical Input,  Prev: Special Characters,  Up: Terminal Modes

17.4.10 Noncanonical Input
--------------------------

In noncanonical input mode, the special editing characters such as ERASE
and KILL are ignored.  The system facilities for the user to edit input
are disabled in noncanonical mode, so that all input characters (unless
they are special for signal or flow-control purposes) are passed to the
application program exactly as typed.  It is up to the application
program to give the user ways to edit the input, if appropriate.

   Noncanonical mode offers special parameters called MIN and TIME for
controlling whether and how long to wait for input to be available.  You
can even use them to avoid ever waiting—to return immediately with
whatever input is available, or with no input.

   The MIN and TIME are stored in elements of the ‘c_cc’ array, which is
a member of the ‘struct termios’ structure.  Each element of this array
has a particular role, and each element has a symbolic constant that
stands for the index of that element.  ‘VMIN’ and ‘VTIME’ are the names
for the indices in the array of the MIN and TIME slots.

 -- Macro: int VMIN

     This is the subscript for the MIN slot in the ‘c_cc’ array.  Thus,
     ‘TERMIOS.c_cc[VMIN]’ is the value itself.

     The MIN slot is only meaningful in noncanonical input mode; it
     specifies the minimum number of bytes that must be available in the
     input queue in order for ‘read’ to return.

 -- Macro: int VTIME

     This is the subscript for the TIME slot in the ‘c_cc’ array.  Thus,
     ‘TERMIOS.c_cc[VTIME]’ is the value itself.

     The TIME slot is only meaningful in noncanonical input mode; it
     specifies how long to wait for input before returning, in units of
     0.1 seconds.

   The MIN and TIME values interact to determine the criterion for when
‘read’ should return; their precise meanings depend on which of them are
nonzero.  There are four possible cases:

   • Both TIME and MIN are nonzero.

     In this case, TIME specifies how long to wait after each input
     character to see if more input arrives.  After the first character
     received, ‘read’ keeps waiting until either MIN bytes have arrived
     in all, or TIME elapses with no further input.

     ‘read’ always blocks until the first character arrives, even if
     TIME elapses first.  ‘read’ can return more than MIN characters if
     more than MIN happen to be in the queue.

   • Both MIN and TIME are zero.

     In this case, ‘read’ always returns immediately with as many
     characters as are available in the queue, up to the number
     requested.  If no input is immediately available, ‘read’ returns a
     value of zero.

   • MIN is zero but TIME has a nonzero value.

     In this case, ‘read’ waits for time TIME for input to become
     available; the availability of a single byte is enough to satisfy
     the read request and cause ‘read’ to return.  When it returns, it
     returns as many characters as are available, up to the number
     requested.  If no input is available before the timer expires,
     ‘read’ returns a value of zero.

   • TIME is zero but MIN has a nonzero value.

     In this case, ‘read’ waits until at least MIN bytes are available
     in the queue.  At that time, ‘read’ returns as many characters as
     are available, up to the number requested.  ‘read’ can return more
     than MIN characters if more than MIN happen to be in the queue.

   What happens if MIN is 50 and you ask to read just 10 bytes?
Normally, ‘read’ waits until there are 50 bytes in the buffer (or, more
generally, the wait condition described above is satisfied), and then
reads 10 of them, leaving the other 40 buffered in the operating system
for a subsequent call to ‘read’.

   *Portability note:* On some systems, the MIN and TIME slots are
actually the same as the EOF and EOL slots.  This causes no serious
problem because the MIN and TIME slots are used only in noncanonical
input and the EOF and EOL slots are used only in canonical input, but it
isn’t very clean.  The GNU C Library allocates separate slots for these
uses.

 -- Function: void cfmakeraw (struct termios *TERMIOS-P)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function provides an easy way to set up ‘*TERMIOS-P’ for what
     has traditionally been called “raw mode” in BSD. This uses
     noncanonical input, and turns off most processing to give an
     unmodified channel to the terminal.

     It does exactly this:
            TERMIOS-P->c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP
                                          |INLCR|IGNCR|ICRNL|IXON);
            TERMIOS-P->c_oflag &= ~OPOST;
            TERMIOS-P->c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
            TERMIOS-P->c_cflag &= ~(CSIZE|PARENB);
            TERMIOS-P->c_cflag |= CS8;


File: libc.info,  Node: BSD Terminal Modes,  Next: Line Control,  Prev: Terminal Modes,  Up: Low-Level Terminal Interface

17.5 BSD Terminal Modes
=======================

The usual way to get and set terminal modes is with the functions
described in *note Terminal Modes::.  However, on some systems you can
use the BSD-derived functions in this section to do some of the same
things.  On many systems, these functions do not exist.  Even with the
GNU C Library, the functions simply fail with ‘errno’ = ‘ENOSYS’ with
many kernels, including Linux.

   The symbols used in this section are declared in ‘sgtty.h’.

 -- Data Type: struct sgttyb

     This structure is an input or output parameter list for ‘gtty’ and
     ‘stty’.

     ‘char sg_ispeed’
          Line speed for input
     ‘char sg_ospeed’
          Line speed for output
     ‘char sg_erase’
          Erase character
     ‘char sg_kill’
          Kill character
     ‘int sg_flags’
          Various flags

 -- Function: int gtty (int FILEDES, struct sgttyb *ATTRIBUTES)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function gets the attributes of a terminal.

     ‘gtty’ sets *ATTRIBUTES to describe the terminal attributes of the
     terminal which is open with file descriptor FILEDES.

 -- Function: int stty (int FILEDES, const struct sgttyb *ATTRIBUTES)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function sets the attributes of a terminal.

     ‘stty’ sets the terminal attributes of the terminal which is open
     with file descriptor FILEDES to those described by *ATTRIBUTES.


File: libc.info,  Node: Line Control,  Next: Noncanon Example,  Prev: BSD Terminal Modes,  Up: Low-Level Terminal Interface

17.6 Line Control Functions
===========================

These functions perform miscellaneous control actions on terminal
devices.  As regards terminal access, they are treated like doing
output: if any of these functions is used by a background process on its
controlling terminal, normally all processes in the process group are
sent a ‘SIGTTOU’ signal.  The exception is if the calling process itself
is ignoring or blocking ‘SIGTTOU’ signals, in which case the operation
is performed and no signal is sent.  *Note Job Control::.

 -- Function: int tcsendbreak (int FILEDES, int DURATION)

     Preliminary: | MT-Unsafe race:tcattr(filedes)/bsd | AS-Unsafe |
     AC-Unsafe corrupt/bsd | *Note POSIX Safety Concepts::.

     This function generates a break condition by transmitting a stream
     of zero bits on the terminal associated with the file descriptor
     FILEDES.  The duration of the break is controlled by the DURATION
     argument.  If zero, the duration is between 0.25 and 0.5 seconds.
     The meaning of a nonzero value depends on the operating system.

     This function does nothing if the terminal is not an asynchronous
     serial data port.

     The return value is normally zero.  In the event of an error, a
     value of -1 is returned.  The following ‘errno’ error conditions
     are defined for this function:

     ‘EBADF’
          The FILEDES is not a valid file descriptor.

     ‘ENOTTY’
          The FILEDES is not associated with a terminal device.

 -- Function: int tcdrain (int FILEDES)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘tcdrain’ function waits until all queued output to the
     terminal FILEDES has been transmitted.

     This function is a cancellation point in multi-threaded programs.
     This is a problem if the thread allocates some resources (like
     memory, file descriptors, semaphores or whatever) at the time
     ‘tcdrain’ is called.  If the thread gets canceled these resources
     stay allocated until the program ends.  To avoid this calls to
     ‘tcdrain’ should be protected using cancellation handlers.

     The return value is normally zero.  In the event of an error, a
     value of -1 is returned.  The following ‘errno’ error conditions
     are defined for this function:

     ‘EBADF’
          The FILEDES is not a valid file descriptor.

     ‘ENOTTY’
          The FILEDES is not associated with a terminal device.

     ‘EINTR’
          The operation was interrupted by delivery of a signal.  *Note
          Interrupted Primitives::.

 -- Function: int tcflush (int FILEDES, int QUEUE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘tcflush’ function is used to clear the input and/or output
     queues associated with the terminal file FILEDES.  The QUEUE
     argument specifies which queue(s) to clear, and can be one of the
     following values:

     ‘TCIFLUSH’

          Clear any input data received, but not yet read.

     ‘TCOFLUSH’

          Clear any output data written, but not yet transmitted.

     ‘TCIOFLUSH’

          Clear both queued input and output.

     The return value is normally zero.  In the event of an error, a
     value of -1 is returned.  The following ‘errno’ error conditions
     are defined for this function:

     ‘EBADF’
          The FILEDES is not a valid file descriptor.

     ‘ENOTTY’
          The FILEDES is not associated with a terminal device.

     ‘EINVAL’
          A bad value was supplied as the QUEUE argument.

     It is unfortunate that this function is named ‘tcflush’, because
     the term “flush” is normally used for quite another
     operation—waiting until all output is transmitted—and using it for
     discarding input or output would be confusing.  Unfortunately, the
     name ‘tcflush’ comes from POSIX and we cannot change it.

 -- Function: int tcflow (int FILEDES, int ACTION)

     Preliminary: | MT-Unsafe race:tcattr(filedes)/bsd | AS-Unsafe |
     AC-Safe | *Note POSIX Safety Concepts::.

     The ‘tcflow’ function is used to perform operations relating to
     XON/XOFF flow control on the terminal file specified by FILEDES.

     The ACTION argument specifies what operation to perform, and can be
     one of the following values:

     ‘TCOOFF’
          Suspend transmission of output.

     ‘TCOON’
          Restart transmission of output.

     ‘TCIOFF’
          Transmit a STOP character.

     ‘TCION’
          Transmit a START character.

     For more information about the STOP and START characters, see *note
     Special Characters::.

     The return value is normally zero.  In the event of an error, a
     value of -1 is returned.  The following ‘errno’ error conditions
     are defined for this function:

     ‘EBADF’
          The FILEDES is not a valid file descriptor.

     ‘ENOTTY’
          The FILEDES is not associated with a terminal device.

     ‘EINVAL’
          A bad value was supplied as the ACTION argument.


File: libc.info,  Node: Noncanon Example,  Next: getpass,  Prev: Line Control,  Up: Low-Level Terminal Interface

17.7 Noncanonical Mode Example
==============================

Here is an example program that shows how you can set up a terminal
device to read single characters in noncanonical input mode, without
echo.


     #include <unistd.h>
     #include <stdio.h>
     #include <stdlib.h>
     #include <termios.h>

     /* Use this variable to remember original terminal attributes. */

     struct termios saved_attributes;

     void
     reset_input_mode (void)
     {
       tcsetattr (STDIN_FILENO, TCSANOW, &saved_attributes);
     }

     void
     set_input_mode (void)
     {
       struct termios tattr;
       char *name;

       /* Make sure stdin is a terminal. */
       if (!isatty (STDIN_FILENO))
         {
           fprintf (stderr, "Not a terminal.\n");
           exit (EXIT_FAILURE);
         }

       /* Save the terminal attributes so we can restore them later. */
       tcgetattr (STDIN_FILENO, &saved_attributes);
       atexit (reset_input_mode);

       /* Set the funny terminal modes. */
       tcgetattr (STDIN_FILENO, &tattr);
       tattr.c_lflag &= ~(ICANON|ECHO); /* Clear ICANON and ECHO. */
       tattr.c_cc[VMIN] = 1;
       tattr.c_cc[VTIME] = 0;
       tcsetattr (STDIN_FILENO, TCSAFLUSH, &tattr);
     }

     int
     main (void)
     {
       char c;

       set_input_mode ();

       while (1)
         {
           read (STDIN_FILENO, &c, 1);
           if (c == '\004')          /* ‘C-d’ */
             break;
           else
             putchar (c);
         }

       return EXIT_SUCCESS;
     }

   This program is careful to restore the original terminal modes before
exiting or terminating with a signal.  It uses the ‘atexit’ function
(*note Cleanups on Exit::) to make sure this is done by ‘exit’.

   The shell is supposed to take care of resetting the terminal modes
when a process is stopped or continued; see *note Job Control::.  But
some existing shells do not actually do this, so you may wish to
establish handlers for job control signals that reset terminal modes.
The above example does so.


File: libc.info,  Node: getpass,  Next: Pseudo-Terminals,  Prev: Noncanon Example,  Up: Low-Level Terminal Interface

17.8 Reading Passphrases
========================

When reading in a passphrase, it is desirable to avoid displaying it on
the screen, to help keep it secret.  The following function handles this
in a convenient way.

 -- Function: char * getpass (const char *PROMPT)

     Preliminary: | MT-Unsafe term | AS-Unsafe heap lock corrupt |
     AC-Unsafe term lock corrupt | *Note POSIX Safety Concepts::.

     ‘getpass’ outputs PROMPT, then reads a string in from the terminal
     without echoing it.  It tries to connect to the real terminal,
     ‘/dev/tty’, if possible, to encourage users not to put plaintext
     passphrases in files; otherwise, it uses ‘stdin’ and ‘stderr’.
     ‘getpass’ also disables the INTR, QUIT, and SUSP characters on the
     terminal using the ‘ISIG’ terminal attribute (*note Local Modes::).
     The terminal is flushed before and after ‘getpass’, so that
     characters of a mistyped passphrase are not accidentally visible.

     In other C libraries, ‘getpass’ may only return the first
     ‘PASS_MAX’ bytes of a passphrase.  The GNU C Library has no limit,
     so ‘PASS_MAX’ is undefined.

     The prototype for this function is in ‘unistd.h’.  ‘PASS_MAX’ would
     be defined in ‘limits.h’.

   This precise set of operations may not suit all possible situations.
In this case, it is recommended that users write their own ‘getpass’
substitute.  For instance, a very simple substitute is as follows:


     #include <termios.h>
     #include <stdio.h>

     ssize_t
     my_getpass (char **lineptr, size_t *n, FILE *stream)
     {
       struct termios old, new;
       int nread;

       /* Turn echoing off and fail if we can’t. */
       if (tcgetattr (fileno (stream), &old) != 0)
         return -1;
       new = old;
       new.c_lflag &= ~ECHO;
       if (tcsetattr (fileno (stream), TCSAFLUSH, &new) != 0)
         return -1;

       /* Read the passphrase */
       nread = getline (lineptr, n, stream);

       /* Restore terminal. */
       (void) tcsetattr (fileno (stream), TCSAFLUSH, &old);

       return nread;
     }

   The substitute takes the same parameters as ‘getline’ (*note Line
Input::); the user must print any prompt desired.


File: libc.info,  Node: Pseudo-Terminals,  Prev: getpass,  Up: Low-Level Terminal Interface

17.9 Pseudo-Terminals
=====================

A "pseudo-terminal" is a special interprocess communication channel that
acts like a terminal.  One end of the channel is called the "master"
side or "master pseudo-terminal device", the other side is called the
"slave" side.  Data written to the master side is received by the slave
side as if it was the result of a user typing at an ordinary terminal,
and data written to the slave side is sent to the master side as if it
was written on an ordinary terminal.

   Pseudo terminals are the way programs like ‘xterm’ and ‘emacs’
implement their terminal emulation functionality.

* Menu:

* Allocation::             Allocating a pseudo terminal.
* Pseudo-Terminal Pairs::  How to open both sides of a
                            pseudo-terminal in a single operation.


File: libc.info,  Node: Allocation,  Next: Pseudo-Terminal Pairs,  Up: Pseudo-Terminals

17.9.1 Allocating Pseudo-Terminals
----------------------------------

This subsection describes functions for allocating a pseudo-terminal,
and for making this pseudo-terminal available for actual use.  These
functions are declared in the header file ‘stdlib.h’.

 -- Function: int getpt (void)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety
     Concepts::.

     The ‘getpt’ function returns a new file descriptor for the next
     available master pseudo-terminal.  The normal return value from
     ‘getpt’ is a non-negative integer file descriptor.  In the case of
     an error, a value of -1 is returned instead.  The following ‘errno’
     conditions are defined for this function:

     ‘ENOENT’
          There are no free master pseudo-terminals available.

     This function is a GNU extension.

 -- Function: int grantpt (int FILEDES)

     Preliminary: | MT-Safe locale | AS-Unsafe dlopen plugin heap lock |
     AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::.

     The ‘grantpt’ function changes the ownership and access permission
     of the slave pseudo-terminal device corresponding to the master
     pseudo-terminal device associated with the file descriptor FILEDES.
     The owner is set from the real user ID of the calling process
     (*note Process Persona::), and the group is set to a special group
     (typically "tty") or from the real group ID of the calling process.
     The access permission is set such that the file is both readable
     and writable by the owner and only writable by the group.

     On some systems this function is implemented by invoking a special
     ‘setuid’ root program (*note How Change Persona::).  As a
     consequence, installing a signal handler for the ‘SIGCHLD’ signal
     (*note Job Control Signals::) may interfere with a call to
     ‘grantpt’.

     The normal return value from ‘grantpt’ is 0; a value of -1 is
     returned in case of failure.  The following ‘errno’ error
     conditions are defined for this function:

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     ‘EINVAL’
          The FILEDES argument is not associated with a master
          pseudo-terminal device.

     ‘EACCES’
          The slave pseudo-terminal device corresponding to the master
          associated with FILEDES could not be accessed.

 -- Function: int unlockpt (int FILEDES)

     Preliminary: | MT-Safe | AS-Unsafe heap/bsd | AC-Unsafe mem fd |
     *Note POSIX Safety Concepts::.

     The ‘unlockpt’ function unlocks the slave pseudo-terminal device
     corresponding to the master pseudo-terminal device associated with
     the file descriptor FILEDES.  On many systems, the slave can only
     be opened after unlocking, so portable applications should always
     call ‘unlockpt’ before trying to open the slave.

     The normal return value from ‘unlockpt’ is 0; a value of -1 is
     returned in case of failure.  The following ‘errno’ error
     conditions are defined for this function:

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     ‘EINVAL’
          The FILEDES argument is not associated with a master
          pseudo-terminal device.

 -- Function: char * ptsname (int FILEDES)

     Preliminary: | MT-Unsafe race:ptsname | AS-Unsafe heap/bsd |
     AC-Unsafe mem fd | *Note POSIX Safety Concepts::.

     If the file descriptor FILEDES is associated with a master
     pseudo-terminal device, the ‘ptsname’ function returns a pointer to
     a statically-allocated, null-terminated string containing the file
     name of the associated slave pseudo-terminal file.  This string
     might be overwritten by subsequent calls to ‘ptsname’.

 -- Function: int ptsname_r (int FILEDES, char *BUF, size_t LEN)

     Preliminary: | MT-Safe | AS-Unsafe heap/bsd | AC-Unsafe mem fd |
     *Note POSIX Safety Concepts::.

     The ‘ptsname_r’ function is similar to the ‘ptsname’ function
     except that it places its result into the user-specified buffer
     starting at BUF with length LEN.

     This function is a GNU extension.

   Typical usage of these functions is illustrated by the following
example:
     int
     open_pty_pair (int *amaster, int *aslave)
     {
       int master, slave;
       char *name;

       master = getpt ();
       if (master < 0)
         return 0;

       if (grantpt (master) < 0 || unlockpt (master) < 0)
         goto close_master;
       name = ptsname (master);
       if (name == NULL)
         goto close_master;

       slave = open (name, O_RDWR);
       if (slave == -1)
         goto close_master;

       *amaster = master;
       *aslave = slave;
       return 1;

     close_slave:
       close (slave);

     close_master:
       close (master);
       return 0;
     }


File: libc.info,  Node: Pseudo-Terminal Pairs,  Prev: Allocation,  Up: Pseudo-Terminals

17.9.2 Opening a Pseudo-Terminal Pair
-------------------------------------

These functions, derived from BSD, are available in the separate
‘libutil’ library, and declared in ‘pty.h’.

 -- Function: int openpty (int *AMASTER, int *ASLAVE, char *NAME, const
          struct termios *TERMP, const struct winsize *WINP)

     Preliminary: | MT-Safe locale | AS-Unsafe dlopen plugin heap lock |
     AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::.

     This function allocates and opens a pseudo-terminal pair, returning
     the file descriptor for the master in *AMASTER, and the file
     descriptor for the slave in *ASLAVE.  If the argument NAME is not a
     null pointer, the file name of the slave pseudo-terminal device is
     stored in ‘*name’.  If TERMP is not a null pointer, the terminal
     attributes of the slave are set to the ones specified in the
     structure that TERMP points to (*note Terminal Modes::).  Likewise,
     if WINP is not a null pointer, the screen size of the slave is set
     to the values specified in the structure that WINP points to.

     The normal return value from ‘openpty’ is 0; a value of -1 is
     returned in case of failure.  The following ‘errno’ conditions are
     defined for this function:

     ‘ENOENT’
          There are no free pseudo-terminal pairs available.

     *Warning:* Using the ‘openpty’ function with NAME not set to ‘NULL’
     is *very dangerous* because it provides no protection against
     overflowing the string NAME.  You should use the ‘ttyname’ function
     on the file descriptor returned in *SLAVE to find out the file name
     of the slave pseudo-terminal device instead.

 -- Function: int forkpty (int *AMASTER, char *NAME, const struct
          termios *TERMP, const struct winsize *WINP)

     Preliminary: | MT-Safe locale | AS-Unsafe dlopen plugin heap lock |
     AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::.

     This function is similar to the ‘openpty’ function, but in
     addition, forks a new process (*note Creating a Process::) and
     makes the newly opened slave pseudo-terminal device the controlling
     terminal (*note Controlling Terminal::) for the child process.

     If the operation is successful, there are then both parent and
     child processes and both see ‘forkpty’ return, but with different
     values: it returns a value of 0 in the child process and returns
     the child’s process ID in the parent process.

     If the allocation of a pseudo-terminal pair or the process creation
     failed, ‘forkpty’ returns a value of -1 in the parent process.

     *Warning:* The ‘forkpty’ function has the same problems with
     respect to the NAME argument as ‘openpty’.


File: libc.info,  Node: Syslog,  Next: Mathematics,  Prev: Low-Level Terminal Interface,  Up: Top

18 Syslog
*********

This chapter describes facilities for issuing and logging messages of
system administration interest.  This chapter has nothing to do with
programs issuing messages to their own users or keeping private logs
(One would typically do that with the facilities described in *note I/O
on Streams::).

   Most systems have a facility called “Syslog” that allows programs to
submit messages of interest to system administrators and can be
configured to pass these messages on in various ways, such as printing
on the console, mailing to a particular person, or recording in a log
file for future reference.

   A program uses the facilities in this chapter to submit such
messages.

* Menu:

* Overview of Syslog::           Overview of a system’s Syslog facility
* Submitting Syslog Messages::   Functions to submit messages to Syslog


File: libc.info,  Node: Overview of Syslog,  Next: Submitting Syslog Messages,  Up: Syslog

18.1 Overview of Syslog
=======================

System administrators have to deal with lots of different kinds of
messages from a plethora of subsystems within each system, and usually
lots of systems as well.  For example, an FTP server might report every
connection it gets.  The kernel might report hardware failures on a disk
drive.  A DNS server might report usage statistics at regular intervals.

   Some of these messages need to be brought to a system administrator’s
attention immediately.  And it may not be just any system administrator
– there may be a particular system administrator who deals with a
particular kind of message.  Other messages just need to be recorded for
future reference if there is a problem.  Still others may need to have
information extracted from them by an automated process that generates
monthly reports.

   To deal with these messages, most Unix systems have a facility called
"Syslog."  It is generally based on a daemon called “Syslogd” Syslogd
listens for messages on a Unix domain socket named ‘/dev/log’.  Based on
classification information in the messages and its configuration file
(usually ‘/etc/syslog.conf’), Syslogd routes them in various ways.  Some
of the popular routings are:

   • Write to the system console
   • Mail to a specific user
   • Write to a log file
   • Pass to another daemon
   • Discard

   Syslogd can also handle messages from other systems.  It listens on
the ‘syslog’ UDP port as well as the local socket for messages.

   Syslog can handle messages from the kernel itself.  But the kernel
doesn’t write to ‘/dev/log’; rather, another daemon (sometimes called
“Klogd”) extracts messages from the kernel and passes them on to Syslog
as any other process would (and it properly identifies them as messages
from the kernel).

   Syslog can even handle messages that the kernel issued before Syslogd
or Klogd was running.  A Linux kernel, for example, stores startup
messages in a kernel message ring and they are normally still there when
Klogd later starts up.  Assuming Syslogd is running by the time Klogd
starts, Klogd then passes everything in the message ring to it.

   In order to classify messages for disposition, Syslog requires any
process that submits a message to it to provide two pieces of
classification information with it:

facility
     This identifies who submitted the message.  There are a small
     number of facilities defined.  The kernel, the mail subsystem, and
     an FTP server are examples of recognized facilities.  For the
     complete list, *Note syslog; vsyslog::.  Keep in mind that these
     are essentially arbitrary classifications.  "Mail subsystem"
     doesn’t have any more meaning than the system administrator gives
     to it.

priority
     This tells how important the content of the message is.  Examples
     of defined priority values are: debug, informational, warning and
     critical.  For the complete list, see *note syslog; vsyslog::.
     Except for the fact that the priorities have a defined order, the
     meaning of each of these priorities is entirely determined by the
     system administrator.

   A “facility/priority” is a number that indicates both the facility
and the priority.

   *Warning:* This terminology is not universal.  Some people use
“level” to refer to the priority and “priority” to refer to the
combination of facility and priority.  A Linux kernel has a concept of a
message “level,” which corresponds both to a Syslog priority and to a
Syslog facility/priority (It can be both because the facility code for
the kernel is zero, and that makes priority and facility/priority the
same value).

   The GNU C Library provides functions to submit messages to Syslog.
They do it by writing to the ‘/dev/log’ socket.  *Note Submitting Syslog
Messages::.

   The GNU C Library functions only work to submit messages to the
Syslog facility on the same system.  To submit a message to the Syslog
facility on another system, use the socket I/O functions to write a UDP
datagram to the ‘syslog’ UDP port on that system.  *Note Sockets::.


File: libc.info,  Node: Submitting Syslog Messages,  Prev: Overview of Syslog,  Up: Syslog

18.2 Submitting Syslog Messages
===============================

The GNU C Library provides functions to submit messages to the Syslog
facility:

* Menu:

* openlog::                      Open connection to Syslog
* syslog; vsyslog::              Submit message to Syslog
* closelog::                     Close connection to Syslog
* setlogmask::                   Cause certain messages to be ignored
* Syslog Example::               Example of all of the above

   These functions only work to submit messages to the Syslog facility
on the same system.  To submit a message to the Syslog facility on
another system, use the socket I/O functions to write a UDP datagram to
the ‘syslog’ UDP port on that system.  *Note Sockets::.


File: libc.info,  Node: openlog,  Next: syslog; vsyslog,  Up: Submitting Syslog Messages

18.2.1 openlog
--------------

The symbols referred to in this section are declared in the file
‘syslog.h’.

 -- Function: void openlog (const char *IDENT, int OPTION, int FACILITY)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock fd | *Note
     POSIX Safety Concepts::.

     ‘openlog’ opens or reopens a connection to Syslog in preparation
     for submitting messages.

     IDENT is an arbitrary identification string which future ‘syslog’
     invocations will prefix to each message.  This is intended to
     identify the source of the message, and people conventionally set
     it to the name of the program that will submit the messages.

     If IDENT is NULL, or if ‘openlog’ is not called, the default
     identification string used in Syslog messages will be the program
     name, taken from argv[0].

     Please note that the string pointer IDENT will be retained
     internally by the Syslog routines.  You must not free the memory
     that IDENT points to.  It is also dangerous to pass a reference to
     an automatic variable since leaving the scope would mean ending the
     lifetime of the variable.  If you want to change the IDENT string,
     you must call ‘openlog’ again; overwriting the string pointed to by
     IDENT is not thread-safe.

     You can cause the Syslog routines to drop the reference to IDENT
     and go back to the default string (the program name taken from
     argv[0]), by calling ‘closelog’: *Note closelog::.

     In particular, if you are writing code for a shared library that
     might get loaded and then unloaded (e.g.  a PAM module), and you
     use ‘openlog’, you must call ‘closelog’ before any point where your
     library might get unloaded, as in this example:

          #include <syslog.h>

          void
          shared_library_function (void)
          {
            openlog ("mylibrary", option, priority);

            syslog (LOG_INFO, "shared library has been invoked");

            closelog ();
          }

     Without the call to ‘closelog’, future invocations of ‘syslog’ by
     the program using the shared library may crash, if the library gets
     unloaded and the memory containing the string ‘"mylibrary"’ becomes
     unmapped.  This is a limitation of the BSD syslog interface.

     ‘openlog’ may or may not open the ‘/dev/log’ socket, depending on
     OPTION.  If it does, it tries to open it and connect it as a stream
     socket.  If that doesn’t work, it tries to open it and connect it
     as a datagram socket.  The socket has the “Close on Exec”
     attribute, so the kernel will close it if the process performs an
     exec.

     You don’t have to use ‘openlog’.  If you call ‘syslog’ without
     having called ‘openlog’, ‘syslog’ just opens the connection
     implicitly and uses defaults for the information in IDENT and
     OPTIONS.

     OPTIONS is a bit string, with the bits as defined by the following
     single bit masks:

     ‘LOG_PERROR’
          If on, ‘openlog’ sets up the connection so that any ‘syslog’
          on this connection writes its message to the calling process’
          Standard Error stream in addition to submitting it to Syslog.
          If off, ‘syslog’ does not write the message to Standard Error.

     ‘LOG_CONS’
          If on, ‘openlog’ sets up the connection so that a ‘syslog’ on
          this connection that fails to submit a message to Syslog
          writes the message instead to system console.  If off,
          ‘syslog’ does not write to the system console (but of course
          Syslog may write messages it receives to the console).

     ‘LOG_PID’
          When on, ‘openlog’ sets up the connection so that a ‘syslog’
          on this connection inserts the calling process’ Process ID
          (PID) into the message.  When off, ‘openlog’ does not insert
          the PID.

     ‘LOG_NDELAY’
          When on, ‘openlog’ opens and connects the ‘/dev/log’ socket.
          When off, a future ‘syslog’ call must open and connect the
          socket.

          *Portability note:* In early systems, the sense of this bit
          was exactly the opposite.

     ‘LOG_ODELAY’
          This bit does nothing.  It exists for backward compatibility.

     If any other bit in OPTIONS is on, the result is undefined.

     FACILITY is the default facility code for this connection.  A
     ‘syslog’ on this connection that specifies default facility causes
     this facility to be associated with the message.  See ‘syslog’ for
     possible values.  A value of zero means the default, which is
     ‘LOG_USER’.

     If a Syslog connection is already open when you call ‘openlog’,
     ‘openlog’ “reopens” the connection.  Reopening is like opening
     except that if you specify zero for the default facility code, the
     default facility code simply remains unchanged and if you specify
     LOG_NDELAY and the socket is already open and connected, ‘openlog’
     just leaves it that way.


File: libc.info,  Node: syslog; vsyslog,  Next: closelog,  Prev: openlog,  Up: Submitting Syslog Messages

18.2.2 syslog, vsyslog
----------------------

The symbols referred to in this section are declared in the file
‘syslog.h’.

 -- Function: void syslog (int FACILITY_PRIORITY, const char *FORMAT, …)

     Preliminary: | MT-Safe env locale | AS-Unsafe corrupt heap lock
     dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety
     Concepts::.

     ‘syslog’ submits a message to the Syslog facility.  It does this by
     writing to the Unix domain socket ‘/dev/log’.

     ‘syslog’ submits the message with the facility and priority
     indicated by FACILITY_PRIORITY.  The macro ‘LOG_MAKEPRI’ generates
     a facility/priority from a facility and a priority, as in the
     following example:

          LOG_MAKEPRI(LOG_USER, LOG_WARNING)

     The possible values for the facility code are (macros):

     ‘LOG_USER’
          A miscellaneous user process
     ‘LOG_MAIL’
          Mail
     ‘LOG_DAEMON’
          A miscellaneous system daemon
     ‘LOG_AUTH’
          Security (authorization)
     ‘LOG_SYSLOG’
          Syslog
     ‘LOG_LPR’
          Central printer
     ‘LOG_NEWS’
          Network news (e.g.  Usenet)
     ‘LOG_UUCP’
          UUCP
     ‘LOG_CRON’
          Cron and At
     ‘LOG_AUTHPRIV’
          Private security (authorization)
     ‘LOG_FTP’
          Ftp server
     ‘LOG_LOCAL0’
          Locally defined
     ‘LOG_LOCAL1’
          Locally defined
     ‘LOG_LOCAL2’
          Locally defined
     ‘LOG_LOCAL3’
          Locally defined
     ‘LOG_LOCAL4’
          Locally defined
     ‘LOG_LOCAL5’
          Locally defined
     ‘LOG_LOCAL6’
          Locally defined
     ‘LOG_LOCAL7’
          Locally defined

     Results are undefined if the facility code is anything else.

     *NB:* ‘syslog’ recognizes one other facility code: that of the
     kernel.  But you can’t specify that facility code with these
     functions.  If you try, it looks the same to ‘syslog’ as if you are
     requesting the default facility.  But you wouldn’t want to anyway,
     because any program that uses the GNU C Library is not the kernel.

     You can use just a priority code as FACILITY_PRIORITY.  In that
     case, ‘syslog’ assumes the default facility established when the
     Syslog connection was opened.  *Note Syslog Example::.

     The possible values for the priority code are (macros):

     ‘LOG_EMERG’
          The message says the system is unusable.
     ‘LOG_ALERT’
          Action on the message must be taken immediately.
     ‘LOG_CRIT’
          The message states a critical condition.
     ‘LOG_ERR’
          The message describes an error.
     ‘LOG_WARNING’
          The message is a warning.
     ‘LOG_NOTICE’
          The message describes a normal but important event.
     ‘LOG_INFO’
          The message is purely informational.
     ‘LOG_DEBUG’
          The message is only for debugging purposes.

     Results are undefined if the priority code is anything else.

     If the process does not presently have a Syslog connection open
     (i.e., it did not call ‘openlog’), ‘syslog’ implicitly opens the
     connection the same as ‘openlog’ would, with the following defaults
     for information that would otherwise be included in an ‘openlog’
     call: The default identification string is the program name.  The
     default default facility is ‘LOG_USER’.  The default for all the
     connection options in OPTIONS is as if those bits were off.
     ‘syslog’ leaves the Syslog connection open.

     If the ‘/dev/log’ socket is not open and connected, ‘syslog’ opens
     and connects it, the same as ‘openlog’ with the ‘LOG_NDELAY’ option
     would.

     ‘syslog’ leaves ‘/dev/log’ open and connected unless its attempt to
     send the message failed, in which case ‘syslog’ closes it (with the
     hope that a future implicit open will restore the Syslog connection
     to a usable state).

     Example:


          #include <syslog.h>
          syslog (LOG_MAKEPRI(LOG_LOCAL1, LOG_ERROR),
                  "Unable to make network connection to %s.  Error=%m", host);

 -- Function: void vsyslog (int FACILITY_PRIORITY, const char *FORMAT,
          va_list ARGLIST)

     Preliminary: | MT-Safe env locale | AS-Unsafe corrupt heap lock
     dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety
     Concepts::.

     This is functionally identical to ‘syslog’, with the BSD style
     variable length argument.


File: libc.info,  Node: closelog,  Next: setlogmask,  Prev: syslog; vsyslog,  Up: Submitting Syslog Messages

18.2.3 closelog
---------------

The symbols referred to in this section are declared in the file
‘syslog.h’.

 -- Function: void closelog (void)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock fd | *Note
     POSIX Safety Concepts::.

     ‘closelog’ closes the current Syslog connection, if there is one.
     This includes closing the ‘/dev/log’ socket, if it is open.
     ‘closelog’ also sets the identification string for Syslog messages
     back to the default, if ‘openlog’ was called with a non-NULL
     argument to IDENT.  The default identification string is the
     program name taken from argv[0].

     If you are writing shared library code that uses ‘openlog’ to
     generate custom syslog output, you should use ‘closelog’ to drop
     the GNU C Library’s internal reference to the IDENT pointer when
     you are done.  Please read the section on ‘openlog’ for more
     information: *Note openlog::.

     ‘closelog’ does not flush any buffers.  You do not have to call
     ‘closelog’ before re-opening a Syslog connection with ‘openlog’.
     Syslog connections are automatically closed on exec or exit.


File: libc.info,  Node: setlogmask,  Next: Syslog Example,  Prev: closelog,  Up: Submitting Syslog Messages

18.2.4 setlogmask
-----------------

The symbols referred to in this section are declared in the file
‘syslog.h’.

 -- Function: int setlogmask (int MASK)

     Preliminary: | MT-Unsafe race:LogMask | AS-Unsafe | AC-Safe | *Note
     POSIX Safety Concepts::.

     ‘setlogmask’ sets a mask (the “logmask”) that determines which
     future ‘syslog’ calls shall be ignored.  If a program has not
     called ‘setlogmask’, ‘syslog’ doesn’t ignore any calls.  You can
     use ‘setlogmask’ to specify that messages of particular priorities
     shall be ignored in the future.

     A ‘setlogmask’ call overrides any previous ‘setlogmask’ call.

     Note that the logmask exists entirely independently of opening and
     closing of Syslog connections.

     Setting the logmask has a similar effect to, but is not the same
     as, configuring Syslog.  The Syslog configuration may cause Syslog
     to discard certain messages it receives, but the logmask causes
     certain messages never to get submitted to Syslog in the first
     place.

     MASK is a bit string with one bit corresponding to each of the
     possible message priorities.  If the bit is on, ‘syslog’ handles
     messages of that priority normally.  If it is off, ‘syslog’
     discards messages of that priority.  Use the message priority
     macros described in *note syslog; vsyslog:: and the ‘LOG_MASK’ to
     construct an appropriate MASK value, as in this example:

          LOG_MASK(LOG_EMERG) | LOG_MASK(LOG_ERROR)

     or

          ~(LOG_MASK(LOG_INFO))

     There is also a ‘LOG_UPTO’ macro, which generates a mask with the
     bits on for a certain priority and all priorities above it:

          LOG_UPTO(LOG_ERROR)

     The unfortunate naming of the macro is due to the fact that
     internally, higher numbers are used for lower message priorities.


File: libc.info,  Node: Syslog Example,  Prev: setlogmask,  Up: Submitting Syslog Messages

18.2.5 Syslog Example
---------------------

Here is an example of ‘openlog’, ‘syslog’, and ‘closelog’:

   This example sets the logmask so that debug and informational
messages get discarded without ever reaching Syslog.  So the second
‘syslog’ in the example does nothing.

     #include <syslog.h>

     setlogmask (LOG_UPTO (LOG_NOTICE));

     openlog ("exampleprog", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);

     syslog (LOG_NOTICE, "Program started by User %d", getuid ());
     syslog (LOG_INFO, "A tree falls in a forest");

     closelog ();


File: libc.info,  Node: Mathematics,  Next: Arithmetic,  Prev: Syslog,  Up: Top

19 Mathematics
**************

This chapter contains information about functions for performing
mathematical computations, such as trigonometric functions.  Most of
these functions have prototypes declared in the header file ‘math.h’.
The complex-valued functions are defined in ‘complex.h’.

   All mathematical functions which take a floating-point argument have
three variants, one each for ‘double’, ‘float’, and ‘long double’
arguments.  The ‘double’ versions are mostly defined in ISO C89.  The
‘float’ and ‘long double’ versions are from the numeric extensions to C
included in ISO C99.

   Which of the three versions of a function should be used depends on
the situation.  For most calculations, the ‘float’ functions are the
fastest.  On the other hand, the ‘long double’ functions have the
highest precision.  ‘double’ is somewhere in between.  It is usually
wise to pick the narrowest type that can accommodate your data.  Not all
machines have a distinct ‘long double’ type; it may be the same as
‘double’.

   The GNU C Library also provides ‘_FloatN’ and ‘_FloatNx’ types.
These types are defined in ISO/IEC TS 18661-3, which extends ISO C and
defines floating-point types that are not machine-dependent.  When such
a type, such as ‘_Float128’, is supported by the GNU C Library, extra
variants for most of the mathematical functions provided for ‘double’,
‘float’, and ‘long double’ are also provided for the supported type.
Throughout this manual, the ‘_FloatN’ and ‘_FloatNx’ variants of these
functions are described along with the ‘double’, ‘float’, and ‘long
double’ variants and they come from ISO/IEC TS 18661-3, unless
explicitly stated otherwise.

   Support for ‘_FloatN’ or ‘_FloatNx’ types is provided for ‘_Float32’,
‘_Float64’ and ‘_Float32x’ on all platforms.  It is also provided for
‘_Float128’ and ‘_Float64x’ on powerpc64le (PowerPC 64-bits
little-endian), x86_64, x86, ia64, aarch64, alpha, mips64, riscv, s390
and sparc.

* Menu:

* Mathematical Constants::      Precise numeric values for often-used
                                 constants.
* Trig Functions::              Sine, cosine, tangent, and friends.
* Inverse Trig Functions::      Arcsine, arccosine, etc.
* Exponents and Logarithms::    Also pow and sqrt.
* Hyperbolic Functions::        sinh, cosh, tanh, etc.
* Special Functions::           Bessel, gamma, erf.
* Errors in Math Functions::    Known Maximum Errors in Math Functions.
* Pseudo-Random Numbers::       Functions for generating pseudo-random
				 numbers.
* FP Function Optimizations::   Fast code or small code.


File: libc.info,  Node: Mathematical Constants,  Next: Trig Functions,  Up: Mathematics

19.1 Predefined Mathematical Constants
======================================

The header ‘math.h’ defines several useful mathematical constants.  All
values are defined as preprocessor macros starting with ‘M_’.  The
values provided are:

‘M_E’
     The base of natural logarithms.
‘M_LOG2E’
     The logarithm to base ‘2’ of ‘M_E’.
‘M_LOG10E’
     The logarithm to base ‘10’ of ‘M_E’.
‘M_LN2’
     The natural logarithm of ‘2’.
‘M_LN10’
     The natural logarithm of ‘10’.
‘M_PI’
     Pi, the ratio of a circle’s circumference to its diameter.
‘M_PI_2’
     Pi divided by two.
‘M_PI_4’
     Pi divided by four.
‘M_1_PI’
     The reciprocal of pi (1/pi)
‘M_2_PI’
     Two times the reciprocal of pi.
‘M_2_SQRTPI’
     Two times the reciprocal of the square root of pi.
‘M_SQRT2’
     The square root of two.
‘M_SQRT1_2’
     The reciprocal of the square root of two (also the square root of
     1/2).

   These constants come from the Unix98 standard and were also available
in 4.4BSD; therefore they are only defined if ‘_XOPEN_SOURCE=500’, or a
more general feature select macro, is defined.  The default set of
features includes these constants.  *Note Feature Test Macros::.

   All values are of type ‘double’.  As an extension, the GNU C Library
also defines these constants with type ‘long double’.  The ‘long double’
macros have a lowercase ‘l’ appended to their names: ‘M_El’, ‘M_PIl’,
and so forth.  These are only available if ‘_GNU_SOURCE’ is defined.

   Likewise, the GNU C Library also defines these constants with the
types ‘_FloatN’ and ‘_FloatNx’ for the machines that have support for
such types enabled (*note Mathematics::) and if ‘_GNU_SOURCE’ is
defined.  When available, the macros names are appended with ‘fN’ or
‘fNx’, such as ‘f128’ for the type ‘_Float128’.

   _Note:_ Some programs use a constant named ‘PI’ which has the same
value as ‘M_PI’.  This constant is not standard; it may have appeared in
some old AT&T headers, and is mentioned in Stroustrup’s book on C++.  It
infringes on the user’s name space, so the GNU C Library does not define
it.  Fixing programs written to expect it is simple: replace ‘PI’ with
‘M_PI’ throughout, or put ‘-DPI=M_PI’ on the compiler command line.


File: libc.info,  Node: Trig Functions,  Next: Inverse Trig Functions,  Prev: Mathematical Constants,  Up: Mathematics

19.2 Trigonometric Functions
============================

These are the familiar ‘sin’, ‘cos’, and ‘tan’ functions.  The arguments
to all of these functions are in units of radians; recall that pi
radians equals 180 degrees.

   The math library normally defines ‘M_PI’ to a ‘double’ approximation
of pi.  If strict ISO and/or POSIX compliance are requested this
constant is not defined, but you can easily define it yourself:

     #define M_PI 3.14159265358979323846264338327

You can also compute the value of pi with the expression ‘acos (-1.0)’.

 -- Function: double sin (double X)
 -- Function: float sinf (float X)
 -- Function: long double sinl (long double X)
 -- Function: _FloatN sinfN (_FloatN X)
 -- Function: _FloatNx sinfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the sine of X, where X is given in radians.
     The return value is in the range ‘-1’ to ‘1’.

 -- Function: double cos (double X)
 -- Function: float cosf (float X)
 -- Function: long double cosl (long double X)
 -- Function: _FloatN cosfN (_FloatN X)
 -- Function: _FloatNx cosfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the cosine of X, where X is given in
     radians.  The return value is in the range ‘-1’ to ‘1’.

 -- Function: double tan (double X)
 -- Function: float tanf (float X)
 -- Function: long double tanl (long double X)
 -- Function: _FloatN tanfN (_FloatN X)
 -- Function: _FloatNx tanfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the tangent of X, where X is given in
     radians.

     Mathematically, the tangent function has singularities at odd
     multiples of pi/2.  If the argument X is too close to one of these
     singularities, ‘tan’ will signal overflow.

   In many applications where ‘sin’ and ‘cos’ are used, the sine and
cosine of the same angle are needed at the same time.  It is more
efficient to compute them simultaneously, so the library provides a
function to do that.

 -- Function: void sincos (double X, double *SINX, double *COSX)
 -- Function: void sincosf (float X, float *SINX, float *COSX)
 -- Function: void sincosl (long double X, long double *SINX, long
          double *COSX)
 -- Function: _FloatN sincosfN (_FloatN X, _FloatN *SINX, _FloatN *COSX)
 -- Function: _FloatNx sincosfNx (_FloatNx X, _FloatNx *SINX, _FloatNx
          *COSX)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the sine of X in ‘*SINX’ and the cosine of X
     in ‘*COSX’, where X is given in radians.  Both values, ‘*SINX’ and
     ‘*COSX’, are in the range of ‘-1’ to ‘1’.

     All these functions, including the ‘_FloatN’ and ‘_FloatNx’
     variants, are GNU extensions.  Portable programs should be prepared
     to cope with their absence.

   ISO C99 defines variants of the trig functions which work on complex
numbers.  The GNU C Library provides these functions, but they are only
useful if your compiler supports the new complex types defined by the
standard.  (As of this writing GCC supports complex numbers, but there
are bugs in the implementation.)

 -- Function: complex double csin (complex double Z)
 -- Function: complex float csinf (complex float Z)
 -- Function: complex long double csinl (complex long double Z)
 -- Function: complex _FloatN csinfN (complex _FloatN Z)
 -- Function: complex _FloatNx csinfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the complex sine of Z.  The mathematical
     definition of the complex sine is

     sin (z) = 1/(2*i) * (exp (z*i) - exp (-z*i)).

 -- Function: complex double ccos (complex double Z)
 -- Function: complex float ccosf (complex float Z)
 -- Function: complex long double ccosl (complex long double Z)
 -- Function: complex _FloatN ccosfN (complex _FloatN Z)
 -- Function: complex _FloatNx ccosfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the complex cosine of Z.  The mathematical
     definition of the complex cosine is

     cos (z) = 1/2 * (exp (z*i) + exp (-z*i))

 -- Function: complex double ctan (complex double Z)
 -- Function: complex float ctanf (complex float Z)
 -- Function: complex long double ctanl (complex long double Z)
 -- Function: complex _FloatN ctanfN (complex _FloatN Z)
 -- Function: complex _FloatNx ctanfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the complex tangent of Z.  The mathematical
     definition of the complex tangent is

     tan (z) = -i * (exp (z*i) - exp (-z*i)) / (exp (z*i) + exp (-z*i))

     The complex tangent has poles at pi/2 + 2n, where n is an integer.
     ‘ctan’ may signal overflow if Z is too close to a pole.


File: libc.info,  Node: Inverse Trig Functions,  Next: Exponents and Logarithms,  Prev: Trig Functions,  Up: Mathematics

19.3 Inverse Trigonometric Functions
====================================

These are the usual arcsine, arccosine and arctangent functions, which
are the inverses of the sine, cosine and tangent functions respectively.

 -- Function: double asin (double X)
 -- Function: float asinf (float X)
 -- Function: long double asinl (long double X)
 -- Function: _FloatN asinfN (_FloatN X)
 -- Function: _FloatNx asinfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute the arcsine of X—that is, the value whose
     sine is X.  The value is in units of radians.  Mathematically,
     there are infinitely many such values; the one actually returned is
     the one between ‘-pi/2’ and ‘pi/2’ (inclusive).

     The arcsine function is defined mathematically only over the domain
     ‘-1’ to ‘1’.  If X is outside the domain, ‘asin’ signals a domain
     error.

 -- Function: double acos (double X)
 -- Function: float acosf (float X)
 -- Function: long double acosl (long double X)
 -- Function: _FloatN acosfN (_FloatN X)
 -- Function: _FloatNx acosfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute the arccosine of X—that is, the value whose
     cosine is X.  The value is in units of radians.  Mathematically,
     there are infinitely many such values; the one actually returned is
     the one between ‘0’ and ‘pi’ (inclusive).

     The arccosine function is defined mathematically only over the
     domain ‘-1’ to ‘1’.  If X is outside the domain, ‘acos’ signals a
     domain error.

 -- Function: double atan (double X)
 -- Function: float atanf (float X)
 -- Function: long double atanl (long double X)
 -- Function: _FloatN atanfN (_FloatN X)
 -- Function: _FloatNx atanfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute the arctangent of X—that is, the value
     whose tangent is X.  The value is in units of radians.
     Mathematically, there are infinitely many such values; the one
     actually returned is the one between ‘-pi/2’ and ‘pi/2’
     (inclusive).

 -- Function: double atan2 (double Y, double X)
 -- Function: float atan2f (float Y, float X)
 -- Function: long double atan2l (long double Y, long double X)
 -- Function: _FloatN atan2fN (_FloatN Y, _FloatN X)
 -- Function: _FloatNx atan2fNx (_FloatNx Y, _FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function computes the arctangent of Y/X, but the signs of both
     arguments are used to determine the quadrant of the result, and X
     is permitted to be zero.  The return value is given in radians and
     is in the range ‘-pi’ to ‘pi’, inclusive.

     If X and Y are coordinates of a point in the plane, ‘atan2’ returns
     the signed angle between the line from the origin to that point and
     the x-axis.  Thus, ‘atan2’ is useful for converting Cartesian
     coordinates to polar coordinates.  (To compute the radial
     coordinate, use ‘hypot’; see *note Exponents and Logarithms::.)

     If both X and Y are zero, ‘atan2’ returns zero.

   ISO C99 defines complex versions of the inverse trig functions.

 -- Function: complex double casin (complex double Z)
 -- Function: complex float casinf (complex float Z)
 -- Function: complex long double casinl (complex long double Z)
 -- Function: complex _FloatN casinfN (complex _FloatN Z)
 -- Function: complex _FloatNx casinfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute the complex arcsine of Z—that is, the value
     whose sine is Z.  The value returned is in radians.

     Unlike the real-valued functions, ‘casin’ is defined for all values
     of Z.

 -- Function: complex double cacos (complex double Z)
 -- Function: complex float cacosf (complex float Z)
 -- Function: complex long double cacosl (complex long double Z)
 -- Function: complex _FloatN cacosfN (complex _FloatN Z)
 -- Function: complex _FloatNx cacosfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute the complex arccosine of Z—that is, the
     value whose cosine is Z.  The value returned is in radians.

     Unlike the real-valued functions, ‘cacos’ is defined for all values
     of Z.

 -- Function: complex double catan (complex double Z)
 -- Function: complex float catanf (complex float Z)
 -- Function: complex long double catanl (complex long double Z)
 -- Function: complex _FloatN catanfN (complex _FloatN Z)
 -- Function: complex _FloatNx catanfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute the complex arctangent of Z—that is, the
     value whose tangent is Z.  The value is in units of radians.


File: libc.info,  Node: Exponents and Logarithms,  Next: Hyperbolic Functions,  Prev: Inverse Trig Functions,  Up: Mathematics

19.4 Exponentiation and Logarithms
==================================

 -- Function: double exp (double X)
 -- Function: float expf (float X)
 -- Function: long double expl (long double X)
 -- Function: _FloatN expfN (_FloatN X)
 -- Function: _FloatNx expfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute ‘e’ (the base of natural logarithms) raised
     to the power X.

     If the magnitude of the result is too large to be representable,
     ‘exp’ signals overflow.

 -- Function: double exp2 (double X)
 -- Function: float exp2f (float X)
 -- Function: long double exp2l (long double X)
 -- Function: _FloatN exp2fN (_FloatN X)
 -- Function: _FloatNx exp2fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute ‘2’ raised to the power X.  Mathematically,
     ‘exp2 (x)’ is the same as ‘exp (x * log (2))’.

 -- Function: double exp10 (double X)
 -- Function: float exp10f (float X)
 -- Function: long double exp10l (long double X)
 -- Function: _FloatN exp10fN (_FloatN X)
 -- Function: _FloatNx exp10fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute ‘10’ raised to the power X.
     Mathematically, ‘exp10 (x)’ is the same as ‘exp (x * log (10))’.

     The ‘exp10’ functions are from TS 18661-4:2015.

 -- Function: double log (double X)
 -- Function: float logf (float X)
 -- Function: long double logl (long double X)
 -- Function: _FloatN logfN (_FloatN X)
 -- Function: _FloatNx logfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions compute the natural logarithm of X.  ‘exp (log
     (X))’ equals X, exactly in mathematics and approximately in C.

     If X is negative, ‘log’ signals a domain error.  If X is zero, it
     returns negative infinity; if X is too close to zero, it may signal
     overflow.

 -- Function: double log10 (double X)
 -- Function: float log10f (float X)
 -- Function: long double log10l (long double X)
 -- Function: _FloatN log10fN (_FloatN X)
 -- Function: _FloatNx log10fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the base-10 logarithm of X.  ‘log10 (X)’
     equals ‘log (X) / log (10)’.

 -- Function: double log2 (double X)
 -- Function: float log2f (float X)
 -- Function: long double log2l (long double X)
 -- Function: _FloatN log2fN (_FloatN X)
 -- Function: _FloatNx log2fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the base-2 logarithm of X.  ‘log2 (X)’
     equals ‘log (X) / log (2)’.

 -- Function: double logb (double X)
 -- Function: float logbf (float X)
 -- Function: long double logbl (long double X)
 -- Function: _FloatN logbfN (_FloatN X)
 -- Function: _FloatNx logbfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions extract the exponent of X and return it as a
     floating-point value.  If ‘FLT_RADIX’ is two, ‘logb’ is equal to
     ‘floor (log2 (x))’, except it’s probably faster.

     If X is de-normalized, ‘logb’ returns the exponent X would have if
     it were normalized.  If X is infinity (positive or negative),
     ‘logb’ returns oo.  If X is zero, ‘logb’ returns oo.  It does not
     signal.

 -- Function: int ilogb (double X)
 -- Function: int ilogbf (float X)
 -- Function: int ilogbl (long double X)
 -- Function: int ilogbfN (_FloatN X)
 -- Function: int ilogbfNx (_FloatNx X)
 -- Function: long int llogb (double X)
 -- Function: long int llogbf (float X)
 -- Function: long int llogbl (long double X)
 -- Function: long int llogbfN (_FloatN X)
 -- Function: long int llogbfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions are equivalent to the corresponding ‘logb’
     functions except that they return signed integer values.  The
     ‘ilogb’, ‘ilogbf’, and ‘ilogbl’ functions are from ISO C99; the
     ‘llogb’, ‘llogbf’, ‘llogbl’ functions are from TS 18661-1:2014; the
     ‘ilogbfN’, ‘ilogbfNx’, ‘llogbfN’, and ‘llogbfNx’ functions are from
     TS 18661-3:2015.

Since integers cannot represent infinity and NaN, ‘ilogb’ instead
returns an integer that can’t be the exponent of a normal floating-point
number.  ‘math.h’ defines constants so you can check for this.

 -- Macro: int FP_ILOGB0

     ‘ilogb’ returns this value if its argument is ‘0’.  The numeric
     value is either ‘INT_MIN’ or ‘-INT_MAX’.

     This macro is defined in ISO C99.

 -- Macro: long int FP_LLOGB0

     ‘llogb’ returns this value if its argument is ‘0’.  The numeric
     value is either ‘LONG_MIN’ or ‘-LONG_MAX’.

     This macro is defined in TS 18661-1:2014.

 -- Macro: int FP_ILOGBNAN

     ‘ilogb’ returns this value if its argument is ‘NaN’.  The numeric
     value is either ‘INT_MIN’ or ‘INT_MAX’.

     This macro is defined in ISO C99.

 -- Macro: long int FP_LLOGBNAN

     ‘llogb’ returns this value if its argument is ‘NaN’.  The numeric
     value is either ‘LONG_MIN’ or ‘LONG_MAX’.

     This macro is defined in TS 18661-1:2014.

   These values are system specific.  They might even be the same.  The
proper way to test the result of ‘ilogb’ is as follows:

     i = ilogb (f);
     if (i == FP_ILOGB0 || i == FP_ILOGBNAN)
       {
         if (isnan (f))
           {
             /* Handle NaN.  */
           }
         else if (f  == 0.0)
           {
             /* Handle 0.0.  */
           }
         else
           {
             /* Some other value with large exponent,
                perhaps +Inf.  */
           }
       }

 -- Function: double pow (double BASE, double POWER)
 -- Function: float powf (float BASE, float POWER)
 -- Function: long double powl (long double BASE, long double POWER)
 -- Function: _FloatN powfN (_FloatN BASE, _FloatN POWER)
 -- Function: _FloatNx powfNx (_FloatNx BASE, _FloatNx POWER)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These are general exponentiation functions, returning BASE raised
     to POWER.

     Mathematically, ‘pow’ would return a complex number when BASE is
     negative and POWER is not an integral value.  ‘pow’ can’t do that,
     so instead it signals a domain error.  ‘pow’ may also underflow or
     overflow the destination type.

 -- Function: double sqrt (double X)
 -- Function: float sqrtf (float X)
 -- Function: long double sqrtl (long double X)
 -- Function: _FloatN sqrtfN (_FloatN X)
 -- Function: _FloatNx sqrtfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the nonnegative square root of X.

     If X is negative, ‘sqrt’ signals a domain error.  Mathematically,
     it should return a complex number.

 -- Function: double cbrt (double X)
 -- Function: float cbrtf (float X)
 -- Function: long double cbrtl (long double X)
 -- Function: _FloatN cbrtfN (_FloatN X)
 -- Function: _FloatNx cbrtfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the cube root of X.  They cannot fail; every
     representable real value has a representable real cube root.

 -- Function: double hypot (double X, double Y)
 -- Function: float hypotf (float X, float Y)
 -- Function: long double hypotl (long double X, long double Y)
 -- Function: _FloatN hypotfN (_FloatN X, _FloatN Y)
 -- Function: _FloatNx hypotfNx (_FloatNx X, _FloatNx Y)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return ‘sqrt (X*X + Y*Y)’.  This is the length of
     the hypotenuse of a right triangle with sides of length X and Y, or
     the distance of the point (X, Y) from the origin.  Using this
     function instead of the direct formula is wise, since the error is
     much smaller.  See also the function ‘cabs’ in *note Absolute
     Value::.

 -- Function: double expm1 (double X)
 -- Function: float expm1f (float X)
 -- Function: long double expm1l (long double X)
 -- Function: _FloatN expm1fN (_FloatN X)
 -- Function: _FloatNx expm1fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return a value equivalent to ‘exp (X) - 1’.  They
     are computed in a way that is accurate even if X is near zero—a
     case where ‘exp (X) - 1’ would be inaccurate owing to subtraction
     of two numbers that are nearly equal.

 -- Function: double log1p (double X)
 -- Function: float log1pf (float X)
 -- Function: long double log1pl (long double X)
 -- Function: _FloatN log1pfN (_FloatN X)
 -- Function: _FloatNx log1pfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return a value equivalent to ‘log (1 + X)’.  They
     are computed in a way that is accurate even if X is near zero.

   ISO C99 defines complex variants of some of the exponentiation and
logarithm functions.

 -- Function: complex double cexp (complex double Z)
 -- Function: complex float cexpf (complex float Z)
 -- Function: complex long double cexpl (complex long double Z)
 -- Function: complex _FloatN cexpfN (complex _FloatN Z)
 -- Function: complex _FloatNx cexpfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return ‘e’ (the base of natural logarithms) raised
     to the power of Z.  Mathematically, this corresponds to the value

     exp (z) = exp (creal (z)) * (cos (cimag (z)) + I * sin (cimag (z)))

 -- Function: complex double clog (complex double Z)
 -- Function: complex float clogf (complex float Z)
 -- Function: complex long double clogl (complex long double Z)
 -- Function: complex _FloatN clogfN (complex _FloatN Z)
 -- Function: complex _FloatNx clogfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the natural logarithm of Z.  Mathematically,
     this corresponds to the value

     log (z) = log (cabs (z)) + I * carg (z)

     ‘clog’ has a pole at 0, and will signal overflow if Z equals or is
     very close to 0.  It is well-defined for all other values of Z.

 -- Function: complex double clog10 (complex double Z)
 -- Function: complex float clog10f (complex float Z)
 -- Function: complex long double clog10l (complex long double Z)
 -- Function: complex _FloatN clog10fN (complex _FloatN Z)
 -- Function: complex _FloatNx clog10fNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the base 10 logarithm of the complex value
     Z.  Mathematically, this corresponds to the value

     log10 (z) = log10 (cabs (z)) + I * carg (z) / log (10)

     All these functions, including the ‘_FloatN’ and ‘_FloatNx’
     variants, are GNU extensions.

 -- Function: complex double csqrt (complex double Z)
 -- Function: complex float csqrtf (complex float Z)
 -- Function: complex long double csqrtl (complex long double Z)
 -- Function: complex _FloatN csqrtfN (_FloatN Z)
 -- Function: complex _FloatNx csqrtfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the complex square root of the argument Z.
     Unlike the real-valued functions, they are defined for all values
     of Z.

 -- Function: complex double cpow (complex double BASE, complex double
          POWER)
 -- Function: complex float cpowf (complex float BASE, complex float
          POWER)
 -- Function: complex long double cpowl (complex long double BASE,
          complex long double POWER)
 -- Function: complex _FloatN cpowfN (complex _FloatN BASE, complex
          _FloatN POWER)
 -- Function: complex _FloatNx cpowfNx (complex _FloatNx BASE, complex
          _FloatNx POWER)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return BASE raised to the power of POWER.  This is
     equivalent to ‘cexp (y * clog (x))’


File: libc.info,  Node: Hyperbolic Functions,  Next: Special Functions,  Prev: Exponents and Logarithms,  Up: Mathematics

19.5 Hyperbolic Functions
=========================

The functions in this section are related to the exponential functions;
see *note Exponents and Logarithms::.

 -- Function: double sinh (double X)
 -- Function: float sinhf (float X)
 -- Function: long double sinhl (long double X)
 -- Function: _FloatN sinhfN (_FloatN X)
 -- Function: _FloatNx sinhfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the hyperbolic sine of X, defined
     mathematically as ‘(exp (X) - exp (-X)) / 2’.  They may signal
     overflow if X is too large.

 -- Function: double cosh (double X)
 -- Function: float coshf (float X)
 -- Function: long double coshl (long double X)
 -- Function: _FloatN coshfN (_FloatN X)
 -- Function: _FloatNx coshfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the hyperbolic cosine of X, defined
     mathematically as ‘(exp (X) + exp (-X)) / 2’.  They may signal
     overflow if X is too large.

 -- Function: double tanh (double X)
 -- Function: float tanhf (float X)
 -- Function: long double tanhl (long double X)
 -- Function: _FloatN tanhfN (_FloatN X)
 -- Function: _FloatNx tanhfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the hyperbolic tangent of X, defined
     mathematically as ‘sinh (X) / cosh (X)’.  They may signal overflow
     if X is too large.

   There are counterparts for the hyperbolic functions which take
complex arguments.

 -- Function: complex double csinh (complex double Z)
 -- Function: complex float csinhf (complex float Z)
 -- Function: complex long double csinhl (complex long double Z)
 -- Function: complex _FloatN csinhfN (complex _FloatN Z)
 -- Function: complex _FloatNx csinhfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the complex hyperbolic sine of Z, defined
     mathematically as ‘(exp (Z) - exp (-Z)) / 2’.

 -- Function: complex double ccosh (complex double Z)
 -- Function: complex float ccoshf (complex float Z)
 -- Function: complex long double ccoshl (complex long double Z)
 -- Function: complex _FloatN ccoshfN (complex _FloatN Z)
 -- Function: complex _FloatNx ccoshfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the complex hyperbolic cosine of Z, defined
     mathematically as ‘(exp (Z) + exp (-Z)) / 2’.

 -- Function: complex double ctanh (complex double Z)
 -- Function: complex float ctanhf (complex float Z)
 -- Function: complex long double ctanhl (complex long double Z)
 -- Function: complex _FloatN ctanhfN (complex _FloatN Z)
 -- Function: complex _FloatNx ctanhfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the complex hyperbolic tangent of Z, defined
     mathematically as ‘csinh (Z) / ccosh (Z)’.

 -- Function: double asinh (double X)
 -- Function: float asinhf (float X)
 -- Function: long double asinhl (long double X)
 -- Function: _FloatN asinhfN (_FloatN X)
 -- Function: _FloatNx asinhfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the inverse hyperbolic sine of X—the value
     whose hyperbolic sine is X.

 -- Function: double acosh (double X)
 -- Function: float acoshf (float X)
 -- Function: long double acoshl (long double X)
 -- Function: _FloatN acoshfN (_FloatN X)
 -- Function: _FloatNx acoshfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the inverse hyperbolic cosine of X—the value
     whose hyperbolic cosine is X.  If X is less than ‘1’, ‘acosh’
     signals a domain error.

 -- Function: double atanh (double X)
 -- Function: float atanhf (float X)
 -- Function: long double atanhl (long double X)
 -- Function: _FloatN atanhfN (_FloatN X)
 -- Function: _FloatNx atanhfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the inverse hyperbolic tangent of X—the
     value whose hyperbolic tangent is X.  If the absolute value of X is
     greater than ‘1’, ‘atanh’ signals a domain error; if it is equal to
     1, ‘atanh’ returns infinity.

 -- Function: complex double casinh (complex double Z)
 -- Function: complex float casinhf (complex float Z)
 -- Function: complex long double casinhl (complex long double Z)
 -- Function: complex _FloatN casinhfN (complex _FloatN Z)
 -- Function: complex _FloatNx casinhfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the inverse complex hyperbolic sine of Z—the
     value whose complex hyperbolic sine is Z.

 -- Function: complex double cacosh (complex double Z)
 -- Function: complex float cacoshf (complex float Z)
 -- Function: complex long double cacoshl (complex long double Z)
 -- Function: complex _FloatN cacoshfN (complex _FloatN Z)
 -- Function: complex _FloatNx cacoshfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the inverse complex hyperbolic cosine of
     Z—the value whose complex hyperbolic cosine is Z.  Unlike the
     real-valued functions, there are no restrictions on the value of Z.

 -- Function: complex double catanh (complex double Z)
 -- Function: complex float catanhf (complex float Z)
 -- Function: complex long double catanhl (complex long double Z)
 -- Function: complex _FloatN catanhfN (complex _FloatN Z)
 -- Function: complex _FloatNx catanhfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the inverse complex hyperbolic tangent of
     Z—the value whose complex hyperbolic tangent is Z.  Unlike the
     real-valued functions, there are no restrictions on the value of Z.


File: libc.info,  Node: Special Functions,  Next: Errors in Math Functions,  Prev: Hyperbolic Functions,  Up: Mathematics

19.6 Special Functions
======================

These are some more exotic mathematical functions which are sometimes
useful.  Currently they only have real-valued versions.

 -- Function: double erf (double X)
 -- Function: float erff (float X)
 -- Function: long double erfl (long double X)
 -- Function: _FloatN erffN (_FloatN X)
 -- Function: _FloatNx erffNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘erf’ returns the error function of X.  The error function is
     defined as
          erf (x) = 2/sqrt(pi) * integral from 0 to x of exp(-t^2) dt

 -- Function: double erfc (double X)
 -- Function: float erfcf (float X)
 -- Function: long double erfcl (long double X)
 -- Function: _FloatN erfcfN (_FloatN X)
 -- Function: _FloatNx erfcfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘erfc’ returns ‘1.0 - erf(X)’, but computed in a fashion that
     avoids round-off error when X is large.

 -- Function: double lgamma (double X)
 -- Function: float lgammaf (float X)
 -- Function: long double lgammal (long double X)
 -- Function: _FloatN lgammafN (_FloatN X)
 -- Function: _FloatNx lgammafNx (_FloatNx X)

     Preliminary: | MT-Unsafe race:signgam | AS-Unsafe | AC-Safe | *Note
     POSIX Safety Concepts::.

     ‘lgamma’ returns the natural logarithm of the absolute value of the
     gamma function of X.  The gamma function is defined as
          gamma (x) = integral from 0 to oo of t^(x-1) e^-t dt

     The sign of the gamma function is stored in the global variable
     SIGNGAM, which is declared in ‘math.h’.  It is ‘1’ if the
     intermediate result was positive or zero, or ‘-1’ if it was
     negative.

     To compute the real gamma function you can use the ‘tgamma’
     function or you can compute the values as follows:
          lgam = lgamma(x);
          gam  = signgam*exp(lgam);

     The gamma function has singularities at the non-positive integers.
     ‘lgamma’ will raise the zero divide exception if evaluated at a
     singularity.

 -- Function: double lgamma_r (double X, int *SIGNP)
 -- Function: float lgammaf_r (float X, int *SIGNP)
 -- Function: long double lgammal_r (long double X, int *SIGNP)
 -- Function: _FloatN lgammafN_r (_FloatN X, int *SIGNP)
 -- Function: _FloatNx lgammafNx_r (_FloatNx X, int *SIGNP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘lgamma_r’ is just like ‘lgamma’, but it stores the sign of the
     intermediate result in the variable pointed to by SIGNP instead of
     in the SIGNGAM global.  This means it is reentrant.

     The ‘lgammafN_r’ and ‘lgammafNx_r’ functions are GNU extensions.

 -- Function: double gamma (double X)
 -- Function: float gammaf (float X)
 -- Function: long double gammal (long double X)

     Preliminary: | MT-Unsafe race:signgam | AS-Unsafe | AC-Safe | *Note
     POSIX Safety Concepts::.

     These functions exist for compatibility reasons.  They are
     equivalent to ‘lgamma’ etc.  It is better to use ‘lgamma’ since for
     one the name reflects better the actual computation, and moreover
     ‘lgamma’ is standardized in ISO C99 while ‘gamma’ is not.

 -- Function: double tgamma (double X)
 -- Function: float tgammaf (float X)
 -- Function: long double tgammal (long double X)
 -- Function: _FloatN tgammafN (_FloatN X)
 -- Function: _FloatNx tgammafNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘tgamma’ applies the gamma function to X.  The gamma function is
     defined as
          gamma (x) = integral from 0 to oo of t^(x-1) e^-t dt

     This function was introduced in ISO C99.  The ‘_FloatN’ and
     ‘_FloatNx’ variants were introduced in ISO/IEC TS 18661-3.

 -- Function: double j0 (double X)
 -- Function: float j0f (float X)
 -- Function: long double j0l (long double X)
 -- Function: _FloatN j0fN (_FloatN X)
 -- Function: _FloatNx j0fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘j0’ returns the Bessel function of the first kind of order 0 of X.
     It may signal underflow if X is too large.

     The ‘_FloatN’ and ‘_FloatNx’ variants are GNU extensions.

 -- Function: double j1 (double X)
 -- Function: float j1f (float X)
 -- Function: long double j1l (long double X)
 -- Function: _FloatN j1fN (_FloatN X)
 -- Function: _FloatNx j1fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘j1’ returns the Bessel function of the first kind of order 1 of X.
     It may signal underflow if X is too large.

     The ‘_FloatN’ and ‘_FloatNx’ variants are GNU extensions.

 -- Function: double jn (int N, double X)
 -- Function: float jnf (int N, float X)
 -- Function: long double jnl (int N, long double X)
 -- Function: _FloatN jnfN (int N, _FloatN X)
 -- Function: _FloatNx jnfNx (int N, _FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘jn’ returns the Bessel function of the first kind of order N of X.
     It may signal underflow if X is too large.

     The ‘_FloatN’ and ‘_FloatNx’ variants are GNU extensions.

 -- Function: double y0 (double X)
 -- Function: float y0f (float X)
 -- Function: long double y0l (long double X)
 -- Function: _FloatN y0fN (_FloatN X)
 -- Function: _FloatNx y0fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘y0’ returns the Bessel function of the second kind of order 0 of
     X.  It may signal underflow if X is too large.  If X is negative,
     ‘y0’ signals a domain error; if it is zero, ‘y0’ signals overflow
     and returns -oo.

     The ‘_FloatN’ and ‘_FloatNx’ variants are GNU extensions.

 -- Function: double y1 (double X)
 -- Function: float y1f (float X)
 -- Function: long double y1l (long double X)
 -- Function: _FloatN y1fN (_FloatN X)
 -- Function: _FloatNx y1fNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘y1’ returns the Bessel function of the second kind of order 1 of
     X.  It may signal underflow if X is too large.  If X is negative,
     ‘y1’ signals a domain error; if it is zero, ‘y1’ signals overflow
     and returns -oo.

     The ‘_FloatN’ and ‘_FloatNx’ variants are GNU extensions.

 -- Function: double yn (int N, double X)
 -- Function: float ynf (int N, float X)
 -- Function: long double ynl (int N, long double X)
 -- Function: _FloatN ynfN (int N, _FloatN X)
 -- Function: _FloatNx ynfNx (int N, _FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘yn’ returns the Bessel function of the second kind of order N of
     X.  It may signal underflow if X is too large.  If X is negative,
     ‘yn’ signals a domain error; if it is zero, ‘yn’ signals overflow
     and returns -oo.

     The ‘_FloatN’ and ‘_FloatNx’ variants are GNU extensions.


File: libc.info,  Node: Errors in Math Functions,  Next: Pseudo-Random Numbers,  Prev: Special Functions,  Up: Mathematics

19.7 Known Maximum Errors in Math Functions
===========================================

This section lists the known errors of the functions in the math
library.  Errors are measured in “units of the last place”.  This is a
measure for the relative error.  For a number z with the representation
d.d…d*2^e (we assume IEEE floating-point numbers with base 2) the ULP is
represented by

     |d.d...d - (z / 2^e)| / 2^(p - 1)

where p is the number of bits in the mantissa of the floating-point
number representation.  Ideally the error for all functions is always
less than 0.5ulps in round-to-nearest mode.  Using rounding bits this is
also possible and normally implemented for the basic operations.  Except
for certain functions such as ‘sqrt’, ‘fma’ and ‘rint’ whose results are
fully specified by reference to corresponding IEEE 754 floating-point
operations, and conversions between strings and floating point, the GNU
C Library does not aim for correctly rounded results for functions in
the math library, and does not aim for correctness in whether “inexact”
exceptions are raised.  Instead, the goals for accuracy of functions
without fully specified results are as follows; some functions have bugs
meaning they do not meet these goals in all cases.  In the future, the
GNU C Library may provide some other correctly rounding functions under
the names such as ‘crsin’ proposed for an extension to ISO C.

   • Each function with a floating-point result behaves as if it
     computes an infinite-precision result that is within a few ulp (in
     both real and complex parts, for functions with complex results) of
     the mathematically correct value of the function (interpreted
     together with ISO C or POSIX semantics for the function in
     question) at the exact value passed as the input.  Exceptions are
     raised appropriately for this value and in accordance with IEEE 754
     / ISO C / POSIX semantics, and it is then rounded according to the
     current rounding direction to the result that is returned to the
     user.  ‘errno’ may also be set (*note Math Error Reporting::).
     (The “inexact” exception may be raised, or not raised, even if this
     is inconsistent with the infinite-precision value.)

   • For the IBM ‘long double’ format, as used on PowerPC GNU/Linux, the
     accuracy goal is weaker for input values not exactly representable
     in 106 bits of precision; it is as if the input value is some value
     within 0.5ulp of the value actually passed, where “ulp” is
     interpreted in terms of a fixed-precision 106-bit mantissa, but not
     necessarily the exact value actually passed with discontiguous
     mantissa bits.

   • For the IBM ‘long double’ format, functions whose results are fully
     specified by reference to corresponding IEEE 754 floating-point
     operations have the same accuracy goals as other functions, but
     with the error bound being the same as that for division (3ulp).
     Furthermore, “inexact” and “underflow” exceptions may be raised for
     all functions for any inputs, even where such exceptions are
     inconsistent with the returned value, since the underlying
     floating-point arithmetic has that property.

   • Functions behave as if the infinite-precision result computed is
     zero, infinity or NaN if and only if that is the mathematically
     correct infinite-precision result.  They behave as if the
     infinite-precision result computed always has the same sign as the
     mathematically correct result.

   • If the mathematical result is more than a few ulp above the
     overflow threshold for the current rounding direction, the value
     returned is the appropriate overflow value for the current rounding
     direction, with the overflow exception raised.

   • If the mathematical result has magnitude well below half the least
     subnormal magnitude, the returned value is either zero or the least
     subnormal (in each case, with the correct sign), according to the
     current rounding direction and with the underflow exception raised.

   • Where the mathematical result underflows (before rounding) and is
     not exactly representable as a floating-point value, the function
     does not behave as if the computed infinite-precision result is an
     exact value in the subnormal range.  This means that the underflow
     exception is raised other than possibly for cases where the
     mathematical result is very close to the underflow threshold and
     the function behaves as if it computes an infinite-precision result
     that does not underflow.  (So there may be spurious underflow
     exceptions in cases where the underflowing result is exact, but not
     missing underflow exceptions in cases where it is inexact.)

   • The GNU C Library does not aim for functions to satisfy other
     properties of the underlying mathematical function, such as
     monotonicity, where not implied by the above goals.

   • All the above applies to both real and complex parts, for complex
     functions.

   Therefore many of the functions in the math library have errors.  The
table lists the maximum error for each function which is exposed by one
of the existing tests in the test suite.  The table tries to cover as
much as possible and list the actual maximum error (or at least a
ballpark figure) but this is often not achieved due to the large search
space.

   The table lists the ULP values for different architectures.
Different architectures have different results since their hardware
support for floating-point operations varies and also the existing
hardware support is different.  Only the round-to-nearest rounding mode
is covered by this table, and vector versions of functions are not
covered.  Functions not listed do not have known errors.


File: libc.info,  Node: Pseudo-Random Numbers,  Next: FP Function Optimizations,  Prev: Errors in Math Functions,  Up: Mathematics

19.8 Pseudo-Random Numbers
==========================

This section describes the GNU facilities for generating a series of
pseudo-random numbers.  The numbers generated are not truly random;
typically, they form a sequence that repeats periodically, with a period
so large that you can ignore it for ordinary purposes.  The random
number generator works by remembering a "seed" value which it uses to
compute the next random number and also to compute a new seed.

   Although the generated numbers look unpredictable within one run of a
program, the sequence of numbers is _exactly the same_ from one run to
the next.  This is because the initial seed is always the same.  This is
convenient when you are debugging a program, but it is unhelpful if you
want the program to behave unpredictably.  If you want a different
pseudo-random series each time your program runs, you must specify a
different seed each time.  For ordinary purposes, basing the seed on the
current time works well.  For random numbers in cryptography, *note
Unpredictable Bytes::.

   You can obtain repeatable sequences of numbers on a particular
machine type by specifying the same initial seed value for the random
number generator.  There is no standard meaning for a particular seed
value; the same seed, used in different C libraries or on different CPU
types, will give you different random numbers.

   The GNU C Library supports the standard ISO C random number functions
plus two other sets derived from BSD and SVID. The BSD and ISO C
functions provide identical, somewhat limited functionality.  If only a
small number of random bits are required, we recommend you use the ISO C
interface, ‘rand’ and ‘srand’.  The SVID functions provide a more
flexible interface, which allows better random number generator
algorithms, provides more random bits (up to 48) per call, and can
provide random floating-point numbers.  These functions are required by
the XPG standard and therefore will be present in all modern Unix
systems.

* Menu:

* ISO Random::                  ‘rand’ and friends.
* BSD Random::                  ‘random’ and friends.
* SVID Random::                 ‘drand48’ and friends.


File: libc.info,  Node: ISO Random,  Next: BSD Random,  Up: Pseudo-Random Numbers

19.8.1 ISO C Random Number Functions
------------------------------------

This section describes the random number functions that are part of the ISO C
standard.

   To use these facilities, you should include the header file
‘stdlib.h’ in your program.

 -- Macro: int RAND_MAX

     The value of this macro is an integer constant representing the
     largest value the ‘rand’ function can return.  In the GNU C
     Library, it is ‘2147483647’, which is the largest signed integer
     representable in 32 bits.  In other libraries, it may be as low as
     ‘32767’.

 -- Function: int rand (void)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     The ‘rand’ function returns the next pseudo-random number in the
     series.  The value ranges from ‘0’ to ‘RAND_MAX’.

 -- Function: void srand (unsigned int SEED)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     This function establishes SEED as the seed for a new series of
     pseudo-random numbers.  If you call ‘rand’ before a seed has been
     established with ‘srand’, it uses the value ‘1’ as a default seed.

     To produce a different pseudo-random series each time your program
     is run, do ‘srand (time (0))’.

   POSIX.1 extended the C standard functions to support reproducible
random numbers in multi-threaded programs.  However, the extension is
badly designed and unsuitable for serious work.

 -- Function: int rand_r (unsigned int *SEED)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function returns a random number in the range 0 to ‘RAND_MAX’
     just as ‘rand’ does.  However, all its state is stored in the SEED
     argument.  This means the RNG’s state can only have as many bits as
     the type ‘unsigned int’ has.  This is far too few to provide a good
     RNG.

     If your program requires a reentrant RNG, we recommend you use the
     reentrant GNU extensions to the SVID random number generator.  The
     POSIX.1 interface should only be used when the GNU extensions are
     not available.


File: libc.info,  Node: BSD Random,  Next: SVID Random,  Prev: ISO Random,  Up: Pseudo-Random Numbers

19.8.2 BSD Random Number Functions
----------------------------------

This section describes a set of random number generation functions that
are derived from BSD. There is no advantage to using these functions
with the GNU C Library; we support them for BSD compatibility only.

   The prototypes for these functions are in ‘stdlib.h’.

 -- Function: long int random (void)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     This function returns the next pseudo-random number in the
     sequence.  The value returned ranges from ‘0’ to ‘2147483647’.

     *NB:* Temporarily this function was defined to return a ‘int32_t’
     value to indicate that the return value always contains 32 bits
     even if ‘long int’ is wider.  The standard demands it differently.
     Users must always be aware of the 32-bit limitation, though.

 -- Function: void srandom (unsigned int SEED)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     The ‘srandom’ function sets the state of the random number
     generator based on the integer SEED.  If you supply a SEED value of
     ‘1’, this will cause ‘random’ to reproduce the default set of
     random numbers.

     To produce a different set of pseudo-random numbers each time your
     program runs, do ‘srandom (time (0))’.

 -- Function: char * initstate (unsigned int SEED, char *STATE, size_t
          SIZE)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     The ‘initstate’ function is used to initialize the random number
     generator state.  The argument STATE is an array of SIZE bytes,
     used to hold the state information.  It is initialized based on
     SEED.  The size must be between 8 and 256 bytes, and should be a
     power of two.  The bigger the STATE array, the better.

     The return value is the previous value of the state information
     array.  You can use this value later as an argument to ‘setstate’
     to restore that state.

 -- Function: char * setstate (char *STATE)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     The ‘setstate’ function restores the random number state
     information STATE.  The argument must have been the result of a
     previous call to INITSTATE or SETSTATE.

     The return value is the previous value of the state information
     array.  You can use this value later as an argument to ‘setstate’
     to restore that state.

     If the function fails the return value is ‘NULL’.

   The four functions described so far in this section all work on a
state which is shared by all threads.  The state is not directly
accessible to the user and can only be modified by these functions.
This makes it hard to deal with situations where each thread should have
its own pseudo-random number generator.

   The GNU C Library contains four additional functions which contain
the state as an explicit parameter and therefore make it possible to
handle thread-local PRNGs.  Besides this there is no difference.  In
fact, the four functions already discussed are implemented internally
using the following interfaces.

   The ‘stdlib.h’ header contains a definition of the following type:

 -- Data Type: struct random_data

     Objects of type ‘struct random_data’ contain the information
     necessary to represent the state of the PRNG. Although a complete
     definition of the type is present the type should be treated as
     opaque.

   The functions modifying the state follow exactly the already
described functions.

 -- Function: int random_r (struct random_data *restrict BUF, int32_t
          *restrict RESULT)

     Preliminary: | MT-Safe race:buf | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The ‘random_r’ function behaves exactly like the ‘random’ function
     except that it uses and modifies the state in the object pointed to
     by the first parameter instead of the global state.

 -- Function: int srandom_r (unsigned int SEED, struct random_data *BUF)

     Preliminary: | MT-Safe race:buf | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The ‘srandom_r’ function behaves exactly like the ‘srandom’
     function except that it uses and modifies the state in the object
     pointed to by the second parameter instead of the global state.

 -- Function: int initstate_r (unsigned int SEED, char *restrict
          STATEBUF, size_t STATELEN, struct random_data *restrict BUF)

     Preliminary: | MT-Safe race:buf | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The ‘initstate_r’ function behaves exactly like the ‘initstate’
     function except that it uses and modifies the state in the object
     pointed to by the fourth parameter instead of the global state.

 -- Function: int setstate_r (char *restrict STATEBUF, struct
          random_data *restrict BUF)

     Preliminary: | MT-Safe race:buf | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The ‘setstate_r’ function behaves exactly like the ‘setstate’
     function except that it uses and modifies the state in the object
     pointed to by the first parameter instead of the global state.


File: libc.info,  Node: SVID Random,  Prev: BSD Random,  Up: Pseudo-Random Numbers

19.8.3 SVID Random Number Function
----------------------------------

The C library on SVID systems contains yet another kind of random number
generator functions.  They use a state of 48 bits of data.  The user can
choose among a collection of functions which return the random bits in
different forms.

   Generally there are two kinds of function.  The first uses a state of
the random number generator which is shared among several functions and
by all threads of the process.  The second requires the user to handle
the state.

   All functions have in common that they use the same congruential
formula with the same constants.  The formula is

     Y = (a * X + c) mod m

where X is the state of the generator at the beginning and Y the state
at the end.  ‘a’ and ‘c’ are constants determining the way the generator
works.  By default they are

     a = 0x5DEECE66D = 25214903917
     c = 0xb = 11

but they can also be changed by the user.  ‘m’ is of course 2^48 since
the state consists of a 48-bit array.

   The prototypes for these functions are in ‘stdlib.h’.

 -- Function: double drand48 (void)

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     This function returns a ‘double’ value in the range of ‘0.0’ to
     ‘1.0’ (exclusive).  The random bits are determined by the global
     state of the random number generator in the C library.

     Since the ‘double’ type according to IEEE 754 has a 52-bit mantissa
     this means 4 bits are not initialized by the random number
     generator.  These are (of course) chosen to be the least
     significant bits and they are initialized to ‘0’.

 -- Function: double erand48 (unsigned short int XSUBI[3])

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     This function returns a ‘double’ value in the range of ‘0.0’ to
     ‘1.0’ (exclusive), similarly to ‘drand48’.  The argument is an
     array describing the state of the random number generator.

     This function can be called subsequently since it updates the array
     to guarantee random numbers.  The array should have been
     initialized before initial use to obtain reproducible results.

 -- Function: long int lrand48 (void)

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘lrand48’ function returns an integer value in the range of ‘0’
     to ‘2^31’ (exclusive).  Even if the size of the ‘long int’ type can
     take more than 32 bits, no higher numbers are returned.  The random
     bits are determined by the global state of the random number
     generator in the C library.

 -- Function: long int nrand48 (unsigned short int XSUBI[3])

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     This function is similar to the ‘lrand48’ function in that it
     returns a number in the range of ‘0’ to ‘2^31’ (exclusive) but the
     state of the random number generator used to produce the random
     bits is determined by the array provided as the parameter to the
     function.

     The numbers in the array are updated afterwards so that subsequent
     calls to this function yield different results (as is expected of a
     random number generator).  The array should have been initialized
     before the first call to obtain reproducible results.

 -- Function: long int mrand48 (void)

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘mrand48’ function is similar to ‘lrand48’.  The only
     difference is that the numbers returned are in the range ‘-2^31’ to
     ‘2^31’ (exclusive).

 -- Function: long int jrand48 (unsigned short int XSUBI[3])

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘jrand48’ function is similar to ‘nrand48’.  The only
     difference is that the numbers returned are in the range ‘-2^31’ to
     ‘2^31’ (exclusive).  For the ‘xsubi’ parameter the same
     requirements are necessary.

   The internal state of the random number generator can be initialized
in several ways.  The methods differ in the completeness of the
information provided.

 -- Function: void srand48 (long int SEEDVAL)

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘srand48’ function sets the most significant 32 bits of the
     internal state of the random number generator to the least
     significant 32 bits of the SEEDVAL parameter.  The lower 16 bits
     are initialized to the value ‘0x330E’.  Even if the ‘long int’ type
     contains more than 32 bits only the lower 32 bits are used.

     Owing to this limitation, initialization of the state of this
     function is not very useful.  But it makes it easy to use a
     construct like ‘srand48 (time (0))’.

     A side-effect of this function is that the values ‘a’ and ‘c’ from
     the internal state, which are used in the congruential formula, are
     reset to the default values given above.  This is of importance
     once the user has called the ‘lcong48’ function (see below).

 -- Function: unsigned short int * seed48 (unsigned short int
          SEED16V[3])

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘seed48’ function initializes all 48 bits of the state of the
     internal random number generator from the contents of the parameter
     SEED16V.  Here the lower 16 bits of the first element of SEED16V
     initialize the least significant 16 bits of the internal state, the
     lower 16 bits of ‘SEED16V[1]’ initialize the mid-order 16 bits of
     the state and the 16 lower bits of ‘SEED16V[2]’ initialize the most
     significant 16 bits of the state.

     Unlike ‘srand48’ this function lets the user initialize all 48 bits
     of the state.

     The value returned by ‘seed48’ is a pointer to an array containing
     the values of the internal state before the change.  This might be
     useful to restart the random number generator at a certain state.
     Otherwise the value can simply be ignored.

     As for ‘srand48’, the values ‘a’ and ‘c’ from the congruential
     formula are reset to the default values.

   There is one more function to initialize the random number generator
which enables you to specify even more information by allowing you to
change the parameters in the congruential formula.

 -- Function: void lcong48 (unsigned short int PARAM[7])

     Preliminary: | MT-Unsafe race:drand48 | AS-Unsafe | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘lcong48’ function allows the user to change the complete state
     of the random number generator.  Unlike ‘srand48’ and ‘seed48’,
     this function also changes the constants in the congruential
     formula.

     From the seven elements in the array PARAM the least significant 16
     bits of the entries ‘PARAM[0]’ to ‘PARAM[2]’ determine the initial
     state, the least significant 16 bits of ‘PARAM[3]’ to ‘PARAM[5]’
     determine the 48 bit constant ‘a’ and ‘PARAM[6]’ determines the
     16-bit value ‘c’.

   All the above functions have in common that they use the global
parameters for the congruential formula.  In multi-threaded programs it
might sometimes be useful to have different parameters in different
threads.  For this reason all the above functions have a counterpart
which works on a description of the random number generator in the
user-supplied buffer instead of the global state.

   Please note that it is no problem if several threads use the global
state if all threads use the functions which take a pointer to an array
containing the state.  The random numbers are computed following the
same loop but if the state in the array is different all threads will
obtain an individual random number generator.

   The user-supplied buffer must be of type ‘struct drand48_data’.  This
type should be regarded as opaque and not manipulated directly.

 -- Function: int drand48_r (struct drand48_data *BUFFER, double
          *RESULT)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     This function is equivalent to the ‘drand48’ function with the
     difference that it does not modify the global random number
     generator parameters but instead the parameters in the buffer
     supplied through the pointer BUFFER.  The random number is returned
     in the variable pointed to by RESULT.

     The return value of the function indicates whether the call
     succeeded.  If the value is less than ‘0’ an error occurred and
     ‘errno’ is set to indicate the problem.

     This function is a GNU extension and should not be used in portable
     programs.

 -- Function: int erand48_r (unsigned short int XSUBI[3], struct
          drand48_data *BUFFER, double *RESULT)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The ‘erand48_r’ function works like ‘erand48’, but in addition it
     takes an argument BUFFER which describes the random number
     generator.  The state of the random number generator is taken from
     the ‘xsubi’ array, the parameters for the congruential formula from
     the global random number generator data.  The random number is
     returned in the variable pointed to by RESULT.

     The return value is non-negative if the call succeeded.

     This function is a GNU extension and should not be used in portable
     programs.

 -- Function: int lrand48_r (struct drand48_data *BUFFER, long int
          *RESULT)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     This function is similar to ‘lrand48’, but in addition it takes a
     pointer to a buffer describing the state of the random number
     generator just like ‘drand48’.

     If the return value of the function is non-negative the variable
     pointed to by RESULT contains the result.  Otherwise an error
     occurred.

     This function is a GNU extension and should not be used in portable
     programs.

 -- Function: int nrand48_r (unsigned short int XSUBI[3], struct
          drand48_data *BUFFER, long int *RESULT)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The ‘nrand48_r’ function works like ‘nrand48’ in that it produces a
     random number in the range ‘0’ to ‘2^31’.  But instead of using the
     global parameters for the congruential formula it uses the
     information from the buffer pointed to by BUFFER.  The state is
     described by the values in XSUBI.

     If the return value is non-negative the variable pointed to by
     RESULT contains the result.

     This function is a GNU extension and should not be used in portable
     programs.

 -- Function: int mrand48_r (struct drand48_data *BUFFER, long int
          *RESULT)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     This function is similar to ‘mrand48’ but like the other reentrant
     functions it uses the random number generator described by the
     value in the buffer pointed to by BUFFER.

     If the return value is non-negative the variable pointed to by
     RESULT contains the result.

     This function is a GNU extension and should not be used in portable
     programs.

 -- Function: int jrand48_r (unsigned short int XSUBI[3], struct
          drand48_data *BUFFER, long int *RESULT)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The ‘jrand48_r’ function is similar to ‘jrand48’.  Like the other
     reentrant functions of this function family it uses the
     congruential formula parameters from the buffer pointed to by
     BUFFER.

     If the return value is non-negative the variable pointed to by
     RESULT contains the result.

     This function is a GNU extension and should not be used in portable
     programs.

   Before any of the above functions are used the buffer of type ‘struct
drand48_data’ should be initialized.  The easiest way to do this is to
fill the whole buffer with null bytes, e.g.  by

     memset (buffer, '\0', sizeof (struct drand48_data));

Using any of the reentrant functions of this family now will
automatically initialize the random number generator to the default
values for the state and the parameters of the congruential formula.

   The other possibility is to use any of the functions which explicitly
initialize the buffer.  Though it might be obvious how to initialize the
buffer from looking at the parameter to the function, it is highly
recommended to use these functions since the result might not always be
what you expect.

 -- Function: int srand48_r (long int SEEDVAL, struct drand48_data
          *BUFFER)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     The description of the random number generator represented by the
     information in BUFFER is initialized similarly to what the function
     ‘srand48’ does.  The state is initialized from the parameter
     SEEDVAL and the parameters for the congruential formula are
     initialized to their default values.

     If the return value is non-negative the function call succeeded.

     This function is a GNU extension and should not be used in portable
     programs.

 -- Function: int seed48_r (unsigned short int SEED16V[3], struct
          drand48_data *BUFFER)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     This function is similar to ‘srand48_r’ but like ‘seed48’ it
     initializes all 48 bits of the state from the parameter SEED16V.

     If the return value is non-negative the function call succeeded.
     It does not return a pointer to the previous state of the random
     number generator like the ‘seed48’ function does.  If the user
     wants to preserve the state for a later re-run s/he can copy the
     whole buffer pointed to by BUFFER.

     This function is a GNU extension and should not be used in portable
     programs.

 -- Function: int lcong48_r (unsigned short int PARAM[7], struct
          drand48_data *BUFFER)

     Preliminary: | MT-Safe race:buffer | AS-Safe | AC-Unsafe corrupt |
     *Note POSIX Safety Concepts::.

     This function initializes all aspects of the random number
     generator described in BUFFER with the data in PARAM.  Here it is
     especially true that the function does more than just copying the
     contents of PARAM and BUFFER.  More work is required and therefore
     it is important to use this function rather than initializing the
     random number generator directly.

     If the return value is non-negative the function call succeeded.

     This function is a GNU extension and should not be used in portable
     programs.


File: libc.info,  Node: FP Function Optimizations,  Prev: Pseudo-Random Numbers,  Up: Mathematics

19.9 Is Fast Code or Small Code preferred?
==========================================

If an application uses many floating point functions it is often the
case that the cost of the function calls themselves is not negligible.
Modern processors can often execute the operations themselves very fast,
but the function call disrupts the instruction pipeline.

   For this reason the GNU C Library provides optimizations for many of
the frequently-used math functions.  When GNU CC is used and the user
activates the optimizer, several new inline functions and macros are
defined.  These new functions and macros have the same names as the
library functions and so are used instead of the latter.  In the case of
inline functions the compiler will decide whether it is reasonable to
use them, and this decision is usually correct.

   This means that no calls to the library functions may be necessary,
and can increase the speed of generated code significantly.  The
drawback is that code size will increase, and the increase is not always
negligible.

   There are two kinds of inline functions: those that give the same
result as the library functions and others that might not set ‘errno’
and might have a reduced precision and/or argument range in comparison
with the library functions.  The latter inline functions are only
available if the flag ‘-ffast-math’ is given to GNU CC.

   In cases where the inline functions and macros are not wanted the
symbol ‘__NO_MATH_INLINES’ should be defined before any system header is
included.  This will ensure that only library functions are used.  Of
course, it can be determined for each file in the project whether giving
this option is preferable or not.

   Not all hardware implements the entire IEEE 754 standard, and even if
it does there may be a substantial performance penalty for using some of
its features.  For example, enabling traps on some processors forces the
FPU to run un-pipelined, which can more than double calculation time.


File: libc.info,  Node: Arithmetic,  Next: Date and Time,  Prev: Mathematics,  Up: Top

20 Arithmetic Functions
***********************

This chapter contains information about functions for doing basic
arithmetic operations, such as splitting a float into its integer and
fractional parts or retrieving the imaginary part of a complex value.
These functions are declared in the header files ‘math.h’ and
‘complex.h’.

* Menu:

* Integers::                    Basic integer types and concepts
* Integer Division::            Integer division with guaranteed rounding.
* Floating Point Numbers::      Basic concepts.  IEEE 754.
* Floating Point Classes::      The five kinds of floating-point number.
* Floating Point Errors::       When something goes wrong in a calculation.
* Rounding::                    Controlling how results are rounded.
* Control Functions::           Saving and restoring the FPU’s state.
* Arithmetic Functions::        Fundamental operations provided by the library.
* Complex Numbers::             The types.  Writing complex constants.
* Operations on Complex::       Projection, conjugation, decomposition.
* Parsing of Numbers::          Converting strings to numbers.
* Printing of Floats::          Converting floating-point numbers to strings.
* System V Number Conversion::  An archaic way to convert numbers to strings.


File: libc.info,  Node: Integers,  Next: Integer Division,  Up: Arithmetic

20.1 Integers
=============

The C language defines several integer data types: integer, short
integer, long integer, and character, all in both signed and unsigned
varieties.  The GNU C compiler extends the language to contain long long
integers as well.

   The C integer types were intended to allow code to be portable among
machines with different inherent data sizes (word sizes), so each type
may have different ranges on different machines.  The problem with this
is that a program often needs to be written for a particular range of
integers, and sometimes must be written for a particular size of
storage, regardless of what machine the program runs on.

   To address this problem, the GNU C Library contains C type
definitions you can use to declare integers that meet your exact needs.
Because the GNU C Library header files are customized to a specific
machine, your program source code doesn’t have to be.

   These ‘typedef’s are in ‘stdint.h’.

   If you require that an integer be represented in exactly N bits, use
one of the following types, with the obvious mapping to bit size and
signedness:

   • int8_t
   • int16_t
   • int32_t
   • int64_t
   • uint8_t
   • uint16_t
   • uint32_t
   • uint64_t

   If your C compiler and target machine do not allow integers of a
certain size, the corresponding above type does not exist.

   If you don’t need a specific storage size, but want the smallest data
structure with _at least_ N bits, use one of these:

   • int_least8_t
   • int_least16_t
   • int_least32_t
   • int_least64_t
   • uint_least8_t
   • uint_least16_t
   • uint_least32_t
   • uint_least64_t

   If you don’t need a specific storage size, but want the data
structure that allows the fastest access while having at least N bits
(and among data structures with the same access speed, the smallest
one), use one of these:

   • int_fast8_t
   • int_fast16_t
   • int_fast32_t
   • int_fast64_t
   • uint_fast8_t
   • uint_fast16_t
   • uint_fast32_t
   • uint_fast64_t

   If you want an integer with the widest range possible on the platform
on which it is being used, use one of the following.  If you use these,
you should write code that takes into account the variable size and
range of the integer.

   • intmax_t
   • uintmax_t

   The GNU C Library also provides macros that tell you the maximum and
minimum possible values for each integer data type.  The macro names
follow these examples: ‘INT32_MAX’, ‘UINT8_MAX’, ‘INT_FAST32_MIN’,
‘INT_LEAST64_MIN’, ‘UINTMAX_MAX’, ‘INTMAX_MAX’, ‘INTMAX_MIN’.  Note that
there are no macros for unsigned integer minima.  These are always zero.
Similiarly, there are macros such as ‘INTMAX_WIDTH’ for the width of
these types.  Those macros for integer type widths come from TS
18661-1:2014.

   There are similar macros for use with C’s built in integer types
which should come with your C compiler.  These are described in *note
Data Type Measurements::.

   Don’t forget you can use the C ‘sizeof’ function with any of these
data types to get the number of bytes of storage each uses.


File: libc.info,  Node: Integer Division,  Next: Floating Point Numbers,  Prev: Integers,  Up: Arithmetic

20.2 Integer Division
=====================

This section describes functions for performing integer division.  These
functions are redundant when GNU CC is used, because in GNU C the ‘/’
operator always rounds towards zero.  But in other C implementations,
‘/’ may round differently with negative arguments.  ‘div’ and ‘ldiv’ are
useful because they specify how to round the quotient: towards zero.
The remainder has the same sign as the numerator.

   These functions are specified to return a result R such that the
value ‘R.quot*DENOMINATOR + R.rem’ equals NUMERATOR.

   To use these facilities, you should include the header file
‘stdlib.h’ in your program.

 -- Data Type: div_t

     This is a structure type used to hold the result returned by the
     ‘div’ function.  It has the following members:

     ‘int quot’
          The quotient from the division.

     ‘int rem’
          The remainder from the division.

 -- Function: div_t div (int NUMERATOR, int DENOMINATOR)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The function ‘div’ computes the quotient and remainder from the
     division of NUMERATOR by DENOMINATOR, returning the result in a
     structure of type ‘div_t’.

     If the result cannot be represented (as in a division by zero), the
     behavior is undefined.

     Here is an example, albeit not a very useful one.

          div_t result;
          result = div (20, -6);

     Now ‘result.quot’ is ‘-3’ and ‘result.rem’ is ‘2’.

 -- Data Type: ldiv_t

     This is a structure type used to hold the result returned by the
     ‘ldiv’ function.  It has the following members:

     ‘long int quot’
          The quotient from the division.

     ‘long int rem’
          The remainder from the division.

     (This is identical to ‘div_t’ except that the components are of
     type ‘long int’ rather than ‘int’.)

 -- Function: ldiv_t ldiv (long int NUMERATOR, long int DENOMINATOR)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘ldiv’ function is similar to ‘div’, except that the arguments
     are of type ‘long int’ and the result is returned as a structure of
     type ‘ldiv_t’.

 -- Data Type: lldiv_t

     This is a structure type used to hold the result returned by the
     ‘lldiv’ function.  It has the following members:

     ‘long long int quot’
          The quotient from the division.

     ‘long long int rem’
          The remainder from the division.

     (This is identical to ‘div_t’ except that the components are of
     type ‘long long int’ rather than ‘int’.)

 -- Function: lldiv_t lldiv (long long int NUMERATOR, long long int
          DENOMINATOR)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘lldiv’ function is like the ‘div’ function, but the arguments
     are of type ‘long long int’ and the result is returned as a
     structure of type ‘lldiv_t’.

     The ‘lldiv’ function was added in ISO C99.

 -- Data Type: imaxdiv_t

     This is a structure type used to hold the result returned by the
     ‘imaxdiv’ function.  It has the following members:

     ‘intmax_t quot’
          The quotient from the division.

     ‘intmax_t rem’
          The remainder from the division.

     (This is identical to ‘div_t’ except that the components are of
     type ‘intmax_t’ rather than ‘int’.)

     See *note Integers:: for a description of the ‘intmax_t’ type.

 -- Function: imaxdiv_t imaxdiv (intmax_t NUMERATOR, intmax_t
          DENOMINATOR)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘imaxdiv’ function is like the ‘div’ function, but the
     arguments are of type ‘intmax_t’ and the result is returned as a
     structure of type ‘imaxdiv_t’.

     See *note Integers:: for a description of the ‘intmax_t’ type.

     The ‘imaxdiv’ function was added in ISO C99.


File: libc.info,  Node: Floating Point Numbers,  Next: Floating Point Classes,  Prev: Integer Division,  Up: Arithmetic

20.3 Floating Point Numbers
===========================

Most computer hardware has support for two different kinds of numbers:
integers (…-3, -2, -1, 0, 1, 2, 3…) and floating-point numbers.
Floating-point numbers have three parts: the "mantissa", the "exponent",
and the "sign bit".  The real number represented by a floating-point
value is given by (s ? -1 : 1) * 2^e * M where s is the sign bit, e the
exponent, and M the mantissa.  *Note Floating Point Concepts::, for
details.  (It is possible to have a different "base" for the exponent,
but all modern hardware uses 2.)

   Floating-point numbers can represent a finite subset of the real
numbers.  While this subset is large enough for most purposes, it is
important to remember that the only reals that can be represented
exactly are rational numbers that have a terminating binary expansion
shorter than the width of the mantissa.  Even simple fractions such as
1/5 can only be approximated by floating point.

   Mathematical operations and functions frequently need to produce
values that are not representable.  Often these values can be
approximated closely enough for practical purposes, but sometimes they
can’t.  Historically there was no way to tell when the results of a
calculation were inaccurate.  Modern computers implement the IEEE 754
standard for numerical computations, which defines a framework for
indicating to the program when the results of calculation are not
trustworthy.  This framework consists of a set of "exceptions" that
indicate why a result could not be represented, and the special values
"infinity" and "not a number" (NaN).


File: libc.info,  Node: Floating Point Classes,  Next: Floating Point Errors,  Prev: Floating Point Numbers,  Up: Arithmetic

20.4 Floating-Point Number Classification Functions
===================================================

ISO C99 defines macros that let you determine what sort of
floating-point number a variable holds.

 -- Macro: int fpclassify (_float-type_ X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This is a generic macro which works on all floating-point types and
     which returns a value of type ‘int’.  The possible values are:

     ‘FP_NAN’

          The floating-point number X is “Not a Number” (*note Infinity
          and NaN::)
     ‘FP_INFINITE’

          The value of X is either plus or minus infinity (*note
          Infinity and NaN::)
     ‘FP_ZERO’

          The value of X is zero.  In floating-point formats like
          IEEE 754, where zero can be signed, this value is also
          returned if X is negative zero.
     ‘FP_SUBNORMAL’

          Numbers whose absolute value is too small to be represented in
          the normal format are represented in an alternate,
          "denormalized" format (*note Floating Point Concepts::).  This
          format is less precise but can represent values closer to
          zero.  ‘fpclassify’ returns this value for values of X in this
          alternate format.
     ‘FP_NORMAL’

          This value is returned for all other values of X.  It
          indicates that there is nothing special about the number.

   ‘fpclassify’ is most useful if more than one property of a number
must be tested.  There are more specific macros which only test one
property at a time.  Generally these macros execute faster than
‘fpclassify’, since there is special hardware support for them.  You
should therefore use the specific macros whenever possible.

 -- Macro: int iscanonical (_float-type_ X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     In some floating-point formats, some values have canonical
     (preferred) and noncanonical encodings (for IEEE interchange binary
     formats, all encodings are canonical).  This macro returns a
     nonzero value if X has a canonical encoding.  It is from TS
     18661-1:2014.

     Note that some formats have multiple encodings of a value which are
     all equally canonical; ‘iscanonical’ returns a nonzero value for
     all such encodings.  Also, formats may have encodings that do not
     correspond to any valid value of the type.  In ISO C terms these
     are "trap representations"; in the GNU C Library, ‘iscanonical’
     returns zero for such encodings.

 -- Macro: int isfinite (_float-type_ X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns a nonzero value if X is finite: not plus or
     minus infinity, and not NaN. It is equivalent to

          (fpclassify (x) != FP_NAN && fpclassify (x) != FP_INFINITE)

     ‘isfinite’ is implemented as a macro which accepts any
     floating-point type.

 -- Macro: int isnormal (_float-type_ X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns a nonzero value if X is finite and normalized.
     It is equivalent to

          (fpclassify (x) == FP_NORMAL)

 -- Macro: int isnan (_float-type_ X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns a nonzero value if X is NaN. It is equivalent to

          (fpclassify (x) == FP_NAN)

 -- Macro: int issignaling (_float-type_ X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns a nonzero value if X is a signaling NaN (sNaN).
     It is from TS 18661-1:2014.

 -- Macro: int issubnormal (_float-type_ X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns a nonzero value if X is subnormal.  It is from
     TS 18661-1:2014.

 -- Macro: int iszero (_float-type_ X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns a nonzero value if X is zero.  It is from TS
     18661-1:2014.

   Another set of floating-point classification functions was provided
by BSD. The GNU C Library also supports these functions; however, we
recommend that you use the ISO C99 macros in new code.  Those are
standard and will be available more widely.  Also, since they are
macros, you do not have to worry about the type of their argument.

 -- Function: int isinf (double X)
 -- Function: int isinff (float X)
 -- Function: int isinfl (long double X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function returns ‘-1’ if X represents negative infinity, ‘1’
     if X represents positive infinity, and ‘0’ otherwise.

 -- Function: int isnan (double X)
 -- Function: int isnanf (float X)
 -- Function: int isnanl (long double X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function returns a nonzero value if X is a “not a number”
     value, and zero otherwise.

     *NB:* The ‘isnan’ macro defined by ISO C99 overrides the BSD
     function.  This is normally not a problem, because the two routines
     behave identically.  However, if you really need to get the BSD
     function for some reason, you can write

          (isnan) (x)

 -- Function: int finite (double X)
 -- Function: int finitef (float X)
 -- Function: int finitel (long double X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function returns a nonzero value if X is neither infinite nor
     a “not a number” value, and zero otherwise.

   *Portability Note:* The functions listed in this section are BSD
extensions.


File: libc.info,  Node: Floating Point Errors,  Next: Rounding,  Prev: Floating Point Classes,  Up: Arithmetic

20.5 Errors in Floating-Point Calculations
==========================================

* Menu:

* FP Exceptions::               IEEE 754 math exceptions and how to detect them.
* Infinity and NaN::            Special values returned by calculations.
* Status bit operations::       Checking for exceptions after the fact.
* Math Error Reporting::        How the math functions report errors.


File: libc.info,  Node: FP Exceptions,  Next: Infinity and NaN,  Up: Floating Point Errors

20.5.1 FP Exceptions
--------------------

The IEEE 754 standard defines five "exceptions" that can occur during a
calculation.  Each corresponds to a particular sort of error, such as
overflow.

   When exceptions occur (when exceptions are "raised", in the language
of the standard), one of two things can happen.  By default the
exception is simply noted in the floating-point "status word", and the
program continues as if nothing had happened.  The operation produces a
default value, which depends on the exception (see the table below).
Your program can check the status word to find out which exceptions
happened.

   Alternatively, you can enable "traps" for exceptions.  In that case,
when an exception is raised, your program will receive the ‘SIGFPE’
signal.  The default action for this signal is to terminate the program.
*Note Signal Handling::, for how you can change the effect of the
signal.

The exceptions defined in IEEE 754 are:

‘Invalid Operation’
     This exception is raised if the given operands are invalid for the
     operation to be performed.  Examples are (see IEEE 754, section 7):
       1. Addition or subtraction: oo - oo.  (But oo + oo = oo).
       2. Multiplication: 0 * oo.
       3. Division: 0/0 or oo/oo.
       4. Remainder: x REM y, where y is zero or x is infinite.
       5. Square root if the operand is less than zero.  More generally,
          any mathematical function evaluated outside its domain
          produces this exception.
       6. Conversion of a floating-point number to an integer or decimal
          string, when the number cannot be represented in the target
          format (due to overflow, infinity, or NaN).
       7. Conversion of an unrecognizable input string.
       8. Comparison via predicates involving < or >, when one or other
          of the operands is NaN. You can prevent this exception by
          using the unordered comparison functions instead; see *note FP
          Comparison Functions::.

     If the exception does not trap, the result of the operation is NaN.

‘Division by Zero’
     This exception is raised when a finite nonzero number is divided by
     zero.  If no trap occurs the result is either +oo or -oo, depending
     on the signs of the operands.

‘Overflow’
     This exception is raised whenever the result cannot be represented
     as a finite value in the precision format of the destination.  If
     no trap occurs the result depends on the sign of the intermediate
     result and the current rounding mode (IEEE 754, section 7.3):
       1. Round to nearest carries all overflows to oo with the sign of
          the intermediate result.
       2. Round toward 0 carries all overflows to the largest
          representable finite number with the sign of the intermediate
          result.
       3. Round toward -oo carries positive overflows to the largest
          representable finite number and negative overflows to -oo.

       4. Round toward oo carries negative overflows to the most
          negative representable finite number and positive overflows to
          oo.

     Whenever the overflow exception is raised, the inexact exception is
     also raised.

‘Underflow’
     The underflow exception is raised when an intermediate result is
     too small to be calculated accurately, or if the operation’s result
     rounded to the destination precision is too small to be normalized.

     When no trap is installed for the underflow exception, underflow is
     signaled (via the underflow flag) only when both tininess and loss
     of accuracy have been detected.  If no trap handler is installed
     the operation continues with an imprecise small value, or zero if
     the destination precision cannot hold the small exact result.

‘Inexact’
     This exception is signalled if a rounded result is not exact (such
     as when calculating the square root of two) or a result overflows
     without an overflow trap.


File: libc.info,  Node: Infinity and NaN,  Next: Status bit operations,  Prev: FP Exceptions,  Up: Floating Point Errors

20.5.2 Infinity and NaN
-----------------------

IEEE 754 floating point numbers can represent positive or negative
infinity, and "NaN" (not a number).  These three values arise from
calculations whose result is undefined or cannot be represented
accurately.  You can also deliberately set a floating-point variable to
any of them, which is sometimes useful.  Some examples of calculations
that produce infinity or NaN:

     1/0 = oo
     log (0) = -oo
     sqrt (-1) = NaN

   When a calculation produces any of these values, an exception also
occurs; see *note FP Exceptions::.

   The basic operations and math functions all accept infinity and NaN
and produce sensible output.  Infinities propagate through calculations
as one would expect: for example, 2 + oo = oo, 4/oo = 0, atan (oo) =
pi/2.  NaN, on the other hand, infects any calculation that involves it.
Unless the calculation would produce the same result no matter what real
value replaced NaN, the result is NaN.

   In comparison operations, positive infinity is larger than all values
except itself and NaN, and negative infinity is smaller than all values
except itself and NaN. NaN is "unordered": it is not equal to, greater
than, or less than anything, _including itself_.  ‘x == x’ is false if
the value of ‘x’ is NaN. You can use this to test whether a value is NaN
or not, but the recommended way to test for NaN is with the ‘isnan’
function (*note Floating Point Classes::).  In addition, ‘<’, ‘>’, ‘<=’,
and ‘>=’ will raise an exception when applied to NaNs.

   ‘math.h’ defines macros that allow you to explicitly set a variable
to infinity or NaN.

 -- Macro: float INFINITY

     An expression representing positive infinity.  It is equal to the
     value produced by mathematical operations like ‘1.0 / 0.0’.
     ‘-INFINITY’ represents negative infinity.

     You can test whether a floating-point value is infinite by
     comparing it to this macro.  However, this is not recommended; you
     should use the ‘isfinite’ macro instead.  *Note Floating Point
     Classes::.

     This macro was introduced in the ISO C99 standard.

 -- Macro: float NAN

     An expression representing a value which is “not a number”.  This
     macro is a GNU extension, available only on machines that support
     the “not a number” value—that is to say, on all machines that
     support IEEE floating point.

     You can use ‘#ifdef NAN’ to test whether the machine supports NaN.
     (Of course, you must arrange for GNU extensions to be visible, such
     as by defining ‘_GNU_SOURCE’, and then you must include ‘math.h’.)

 -- Macro: float SNANF
 -- Macro: double SNAN
 -- Macro: long double SNANL
 -- Macro: _FloatN SNANFN
 -- Macro: _FloatNx SNANFNx

     These macros, defined by TS 18661-1:2014 and TS 18661-3:2015, are
     constant expressions for signaling NaNs.

 -- Macro: int FE_SNANS_ALWAYS_SIGNAL

     This macro, defined by TS 18661-1:2014, is defined to ‘1’ in
     ‘fenv.h’ to indicate that functions and operations with signaling
     NaN inputs and floating-point results always raise the invalid
     exception and return a quiet NaN, even in cases (such as ‘fmax’,
     ‘hypot’ and ‘pow’) where a quiet NaN input can produce a non-NaN
     result.  Because some compiler optimizations may not handle
     signaling NaNs correctly, this macro is only defined if compiler
     support for signaling NaNs is enabled.  That support can be enabled
     with the GCC option ‘-fsignaling-nans’.

   IEEE 754 also allows for another unusual value: negative zero.  This
value is produced when you divide a positive number by negative
infinity, or when a negative result is smaller than the limits of
representation.


File: libc.info,  Node: Status bit operations,  Next: Math Error Reporting,  Prev: Infinity and NaN,  Up: Floating Point Errors

20.5.3 Examining the FPU status word
------------------------------------

ISO C99 defines functions to query and manipulate the floating-point
status word.  You can use these functions to check for untrapped
exceptions when it’s convenient, rather than worrying about them in the
middle of a calculation.

   These constants represent the various IEEE 754 exceptions.  Not all
FPUs report all the different exceptions.  Each constant is defined if
and only if the FPU you are compiling for supports that exception, so
you can test for FPU support with ‘#ifdef’.  They are defined in
‘fenv.h’.

‘FE_INEXACT’

     The inexact exception.
‘FE_DIVBYZERO’

     The divide by zero exception.
‘FE_UNDERFLOW’

     The underflow exception.
‘FE_OVERFLOW’

     The overflow exception.
‘FE_INVALID’

     The invalid exception.

   The macro ‘FE_ALL_EXCEPT’ is the bitwise OR of all exception macros
which are supported by the FP implementation.

   These functions allow you to clear exception flags, test for
exceptions, and save and restore the set of exceptions flagged.

 -- Function: int feclearexcept (int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe !posix | AC-Safe !posix | *Note
     POSIX Safety Concepts::.

     This function clears all of the supported exception flags indicated
     by EXCEPTS.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

 -- Function: int feraiseexcept (int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function raises the supported exceptions indicated by EXCEPTS.
     If more than one exception bit in EXCEPTS is set the order in which
     the exceptions are raised is undefined except that overflow
     (‘FE_OVERFLOW’) or underflow (‘FE_UNDERFLOW’) are raised before
     inexact (‘FE_INEXACT’).  Whether for overflow or underflow the
     inexact exception is also raised is also implementation dependent.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

 -- Function: int fesetexcept (int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function sets the supported exception flags indicated by
     EXCEPTS, like ‘feraiseexcept’, but without causing enabled traps to
     be taken.  ‘fesetexcept’ is from TS 18661-1:2014.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

 -- Function: int fetestexcept (int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Test whether the exception flags indicated by the parameter EXCEPT
     are currently set.  If any of them are, a nonzero value is returned
     which specifies which exceptions are set.  Otherwise the result is
     zero.

   To understand these functions, imagine that the status word is an
integer variable named STATUS.  ‘feclearexcept’ is then equivalent to
‘status &= ~excepts’ and ‘fetestexcept’ is equivalent to ‘(status &
excepts)’.  The actual implementation may be very different, of course.

   Exception flags are only cleared when the program explicitly requests
it, by calling ‘feclearexcept’.  If you want to check for exceptions
from a set of calculations, you should clear all the flags first.  Here
is a simple example of the way to use ‘fetestexcept’:

     {
       double f;
       int raised;
       feclearexcept (FE_ALL_EXCEPT);
       f = compute ();
       raised = fetestexcept (FE_OVERFLOW | FE_INVALID);
       if (raised & FE_OVERFLOW) { /* … */ }
       if (raised & FE_INVALID) { /* … */ }
       /* … */
     }

   You cannot explicitly set bits in the status word.  You can, however,
save the entire status word and restore it later.  This is done with the
following functions:

 -- Function: int fegetexceptflag (fexcept_t *FLAGP, int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function stores in the variable pointed to by FLAGP an
     implementation-defined value representing the current setting of
     the exception flags indicated by EXCEPTS.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

 -- Function: int fesetexceptflag (const fexcept_t *FLAGP, int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function restores the flags for the exceptions indicated by
     EXCEPTS to the values stored in the variable pointed to by FLAGP.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

   Note that the value stored in ‘fexcept_t’ bears no resemblance to the
bit mask returned by ‘fetestexcept’.  The type may not even be an
integer.  Do not attempt to modify an ‘fexcept_t’ variable.

 -- Function: int fetestexceptflag (const fexcept_t *FLAGP, int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Test whether the exception flags indicated by the parameter EXCEPTS
     are set in the variable pointed to by FLAGP.  If any of them are, a
     nonzero value is returned which specifies which exceptions are set.
     Otherwise the result is zero.  ‘fetestexceptflag’ is from TS
     18661-1:2014.


File: libc.info,  Node: Math Error Reporting,  Prev: Status bit operations,  Up: Floating Point Errors

20.5.4 Error Reporting by Mathematical Functions
------------------------------------------------

Many of the math functions are defined only over a subset of the real or
complex numbers.  Even if they are mathematically defined, their result
may be larger or smaller than the range representable by their return
type without loss of accuracy.  These are known as "domain errors",
"overflows", and "underflows", respectively.  Math functions do several
things when one of these errors occurs.  In this manual we will refer to
the complete response as "signalling" a domain error, overflow, or
underflow.

   When a math function suffers a domain error, it raises the invalid
exception and returns NaN. It also sets ‘errno’ to ‘EDOM’; this is for
compatibility with old systems that do not support IEEE 754 exception
handling.  Likewise, when overflow occurs, math functions raise the
overflow exception and, in the default rounding mode, return oo or -oo
as appropriate (in other rounding modes, the largest finite value of the
appropriate sign is returned when appropriate for that rounding mode).
They also set ‘errno’ to ‘ERANGE’ if returning oo or -oo; ‘errno’ may or
may not be set to ‘ERANGE’ when a finite value is returned on overflow.
When underflow occurs, the underflow exception is raised, and zero
(appropriately signed) or a subnormal value, as appropriate for the
mathematical result of the function and the rounding mode, is returned.
‘errno’ may be set to ‘ERANGE’, but this is not guaranteed; it is
intended that the GNU C Library should set it when the underflow is to
an appropriately signed zero, but not necessarily for other underflows.

   When a math function has an argument that is a signaling NaN, the GNU
C Library does not consider this a domain error, so ‘errno’ is
unchanged, but the invalid exception is still raised (except for a few
functions that are specified to handle signaling NaNs differently).

   Some of the math functions are defined mathematically to result in a
complex value over parts of their domains.  The most familiar example of
this is taking the square root of a negative number.  The complex math
functions, such as ‘csqrt’, will return the appropriate complex value in
this case.  The real-valued functions, such as ‘sqrt’, will signal a
domain error.

   Some older hardware does not support infinities.  On that hardware,
overflows instead return a particular very large number (usually the
largest representable number).  ‘math.h’ defines macros you can use to
test for overflow on both old and new hardware.

 -- Macro: double HUGE_VAL
 -- Macro: float HUGE_VALF
 -- Macro: long double HUGE_VALL
 -- Macro: _FloatN HUGE_VAL_FN
 -- Macro: _FloatNx HUGE_VAL_FNx

     An expression representing a particular very large number.  On
     machines that use IEEE 754 floating point format, ‘HUGE_VAL’ is
     infinity.  On other machines, it’s typically the largest positive
     number that can be represented.

     Mathematical functions return the appropriately typed version of
     ‘HUGE_VAL’ or ‘−HUGE_VAL’ when the result is too large to be
     represented.


File: libc.info,  Node: Rounding,  Next: Control Functions,  Prev: Floating Point Errors,  Up: Arithmetic

20.6 Rounding Modes
===================

Floating-point calculations are carried out internally with extra
precision, and then rounded to fit into the destination type.  This
ensures that results are as precise as the input data.  IEEE 754 defines
four possible rounding modes:

Round to nearest.
     This is the default mode.  It should be used unless there is a
     specific need for one of the others.  In this mode results are
     rounded to the nearest representable value.  If the result is
     midway between two representable values, the even representable is
     chosen.  "Even" here means the lowest-order bit is zero.  This
     rounding mode prevents statistical bias and guarantees numeric
     stability: round-off errors in a lengthy calculation will remain
     smaller than half of ‘FLT_EPSILON’.

Round toward plus Infinity.
     All results are rounded to the smallest representable value which
     is greater than the result.

Round toward minus Infinity.
     All results are rounded to the largest representable value which is
     less than the result.

Round toward zero.
     All results are rounded to the largest representable value whose
     magnitude is less than that of the result.  In other words, if the
     result is negative it is rounded up; if it is positive, it is
     rounded down.

‘fenv.h’ defines constants which you can use to refer to the various
rounding modes.  Each one will be defined if and only if the FPU
supports the corresponding rounding mode.

‘FE_TONEAREST’

     Round to nearest.

‘FE_UPWARD’

     Round toward +oo.

‘FE_DOWNWARD’

     Round toward -oo.

‘FE_TOWARDZERO’

     Round toward zero.

   Underflow is an unusual case.  Normally, IEEE 754 floating point
numbers are always normalized (*note Floating Point Concepts::).
Numbers smaller than 2^r (where r is the minimum exponent,
‘FLT_MIN_RADIX-1’ for FLOAT) cannot be represented as normalized
numbers.  Rounding all such numbers to zero or 2^r would cause some
algorithms to fail at 0.  Therefore, they are left in denormalized form.
That produces loss of precision, since some bits of the mantissa are
stolen to indicate the decimal point.

   If a result is too small to be represented as a denormalized number,
it is rounded to zero.  However, the sign of the result is preserved; if
the calculation was negative, the result is "negative zero".  Negative
zero can also result from some operations on infinity, such as 4/-oo.

   At any time, one of the above four rounding modes is selected.  You
can find out which one with this function:

 -- Function: int fegetround (void)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Returns the currently selected rounding mode, represented by one of
     the values of the defined rounding mode macros.

To change the rounding mode, use this function:

 -- Function: int fesetround (int ROUND)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Changes the currently selected rounding mode to ROUND.  If ROUND
     does not correspond to one of the supported rounding modes nothing
     is changed.  ‘fesetround’ returns zero if it changed the rounding
     mode, or a nonzero value if the mode is not supported.

   You should avoid changing the rounding mode if possible.  It can be
an expensive operation; also, some hardware requires you to compile your
program differently for it to work.  The resulting code may run slower.
See your compiler documentation for details.


File: libc.info,  Node: Control Functions,  Next: Arithmetic Functions,  Prev: Rounding,  Up: Arithmetic

20.7 Floating-Point Control Functions
=====================================

IEEE 754 floating-point implementations allow the programmer to decide
whether traps will occur for each of the exceptions, by setting bits in
the "control word".  In C, traps result in the program receiving the
‘SIGFPE’ signal; see *note Signal Handling::.

   *NB:* IEEE 754 says that trap handlers are given details of the
exceptional situation, and can set the result value.  C signals do not
provide any mechanism to pass this information back and forth.  Trapping
exceptions in C is therefore not very useful.

   It is sometimes necessary to save the state of the floating-point
unit while you perform some calculation.  The library provides functions
which save and restore the exception flags, the set of exceptions that
generate traps, and the rounding mode.  This information is known as the
"floating-point environment".

   The functions to save and restore the floating-point environment all
use a variable of type ‘fenv_t’ to store information.  This type is
defined in ‘fenv.h’.  Its size and contents are implementation-defined.
You should not attempt to manipulate a variable of this type directly.

   To save the state of the FPU, use one of these functions:

 -- Function: int fegetenv (fenv_t *ENVP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Store the floating-point environment in the variable pointed to by
     ENVP.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

 -- Function: int feholdexcept (fenv_t *ENVP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Store the current floating-point environment in the object pointed
     to by ENVP.  Then clear all exception flags, and set the FPU to
     trap no exceptions.  Not all FPUs support trapping no exceptions;
     if ‘feholdexcept’ cannot set this mode, it returns nonzero value.
     If it succeeds, it returns zero.

   The functions which restore the floating-point environment can take
these kinds of arguments:

   • Pointers to ‘fenv_t’ objects, which were initialized previously by
     a call to ‘fegetenv’ or ‘feholdexcept’.
   • The special macro ‘FE_DFL_ENV’ which represents the floating-point
     environment as it was available at program start.
   • Implementation defined macros with names starting with ‘FE_’ and
     having type ‘fenv_t *’.

     If possible, the GNU C Library defines a macro ‘FE_NOMASK_ENV’
     which represents an environment where every exception raised causes
     a trap to occur.  You can test for this macro using ‘#ifdef’.  It
     is only defined if ‘_GNU_SOURCE’ is defined.

     Some platforms might define other predefined environments.

To set the floating-point environment, you can use either of these
functions:

 -- Function: int fesetenv (const fenv_t *ENVP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Set the floating-point environment to that described by ENVP.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

 -- Function: int feupdateenv (const fenv_t *ENVP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Like ‘fesetenv’, this function sets the floating-point environment
     to that described by ENVP.  However, if any exceptions were flagged
     in the status word before ‘feupdateenv’ was called, they remain
     flagged after the call.  In other words, after ‘feupdateenv’ is
     called, the status word is the bitwise OR of the previous status
     word and the one saved in ENVP.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

TS 18661-1:2014 defines additional functions to save and restore
floating-point control modes (such as the rounding mode and whether
traps are enabled) while leaving other status (such as raised flags)
unchanged.

   The special macro ‘FE_DFL_MODE’ may be passed to ‘fesetmode’.  It
represents the floating-point control modes at program start.

 -- Function: int fegetmode (femode_t *MODEP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Store the floating-point control modes in the variable pointed to
     by MODEP.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

 -- Function: int fesetmode (const femode_t *MODEP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Set the floating-point control modes to those described by MODEP.

     The function returns zero in case the operation was successful, a
     non-zero value otherwise.

To control for individual exceptions if raising them causes a trap to
occur, you can use the following two functions.

   *Portability Note:* These functions are all GNU extensions.

 -- Function: int feenableexcept (int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function enables traps for each of the exceptions as indicated
     by the parameter EXCEPTS.  The individual exceptions are described
     in *note Status bit operations::.  Only the specified exceptions
     are enabled, the status of the other exceptions is not changed.

     The function returns the previous enabled exceptions in case the
     operation was successful, ‘-1’ otherwise.

 -- Function: int fedisableexcept (int EXCEPTS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function disables traps for each of the exceptions as
     indicated by the parameter EXCEPTS.  The individual exceptions are
     described in *note Status bit operations::.  Only the specified
     exceptions are disabled, the status of the other exceptions is not
     changed.

     The function returns the previous enabled exceptions in case the
     operation was successful, ‘-1’ otherwise.

 -- Function: int fegetexcept (void)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The function returns a bitmask of all currently enabled exceptions.
     It returns ‘-1’ in case of failure.


File: libc.info,  Node: Arithmetic Functions,  Next: Complex Numbers,  Prev: Control Functions,  Up: Arithmetic

20.8 Arithmetic Functions
=========================

The C library provides functions to do basic operations on
floating-point numbers.  These include absolute value, maximum and
minimum, normalization, bit twiddling, rounding, and a few others.

* Menu:

* Absolute Value::              Absolute values of integers and floats.
* Normalization Functions::     Extracting exponents and putting them back.
* Rounding Functions::          Rounding floats to integers.
* Remainder Functions::         Remainders on division, precisely defined.
* FP Bit Twiddling::            Sign bit adjustment.  Adding epsilon.
* FP Comparison Functions::     Comparisons without risk of exceptions.
* Misc FP Arithmetic::          Max, min, positive difference, multiply-add.


File: libc.info,  Node: Absolute Value,  Next: Normalization Functions,  Up: Arithmetic Functions

20.8.1 Absolute Value
---------------------

These functions are provided for obtaining the "absolute value" (or
"magnitude") of a number.  The absolute value of a real number X is X if
X is positive, −X if X is negative.  For a complex number Z, whose real
part is X and whose imaginary part is Y, the absolute value is
‘sqrt (X*X + Y*Y)’.

   Prototypes for ‘abs’, ‘labs’ and ‘llabs’ are in ‘stdlib.h’; ‘imaxabs’
is declared in ‘inttypes.h’; the ‘fabs’ functions are declared in
‘math.h’; the ‘cabs’ functions are declared in ‘complex.h’.

 -- Function: int abs (int NUMBER)
 -- Function: long int labs (long int NUMBER)
 -- Function: long long int llabs (long long int NUMBER)
 -- Function: intmax_t imaxabs (intmax_t NUMBER)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the absolute value of NUMBER.

     Most computers use a two’s complement integer representation, in
     which the absolute value of ‘INT_MIN’ (the smallest possible ‘int’)
     cannot be represented; thus, ‘abs (INT_MIN)’ is not defined.

     ‘llabs’ and ‘imaxdiv’ are new to ISO C99.

     See *note Integers:: for a description of the ‘intmax_t’ type.

 -- Function: double fabs (double NUMBER)
 -- Function: float fabsf (float NUMBER)
 -- Function: long double fabsl (long double NUMBER)
 -- Function: _FloatN fabsfN (_FloatN NUMBER)
 -- Function: _FloatNx fabsfNx (_FloatNx NUMBER)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function returns the absolute value of the floating-point
     number NUMBER.

 -- Function: double cabs (complex double Z)
 -- Function: float cabsf (complex float Z)
 -- Function: long double cabsl (complex long double Z)
 -- Function: _FloatN cabsfN (complex _FloatN Z)
 -- Function: _FloatNx cabsfNx (complex _FloatNx Z)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the absolute value of the complex number Z
     (*note Complex Numbers::).  The absolute value of a complex number
     is:

          sqrt (creal (Z) * creal (Z) + cimag (Z) * cimag (Z))

     This function should always be used instead of the direct formula
     because it takes special care to avoid losing precision.  It may
     also take advantage of hardware support for this operation.  See
     ‘hypot’ in *note Exponents and Logarithms::.


File: libc.info,  Node: Normalization Functions,  Next: Rounding Functions,  Prev: Absolute Value,  Up: Arithmetic Functions

20.8.2 Normalization Functions
------------------------------

The functions described in this section are primarily provided as a way
to efficiently perform certain low-level manipulations on floating point
numbers that are represented internally using a binary radix; see *note
Floating Point Concepts::.  These functions are required to have
equivalent behavior even if the representation does not use a radix of
2, but of course they are unlikely to be particularly efficient in those
cases.

   All these functions are declared in ‘math.h’.

 -- Function: double frexp (double VALUE, int *EXPONENT)
 -- Function: float frexpf (float VALUE, int *EXPONENT)
 -- Function: long double frexpl (long double VALUE, int *EXPONENT)
 -- Function: _FloatN frexpfN (_FloatN VALUE, int *EXPONENT)
 -- Function: _FloatNx frexpfNx (_FloatNx VALUE, int *EXPONENT)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions are used to split the number VALUE into a
     normalized fraction and an exponent.

     If the argument VALUE is not zero, the return value is VALUE times
     a power of two, and its magnitude is always in the range 1/2
     (inclusive) to 1 (exclusive).  The corresponding exponent is stored
     in ‘*EXPONENT’; the return value multiplied by 2 raised to this
     exponent equals the original number VALUE.

     For example, ‘frexp (12.8, &exponent)’ returns ‘0.8’ and stores ‘4’
     in ‘exponent’.

     If VALUE is zero, then the return value is zero and zero is stored
     in ‘*EXPONENT’.

 -- Function: double ldexp (double VALUE, int EXPONENT)
 -- Function: float ldexpf (float VALUE, int EXPONENT)
 -- Function: long double ldexpl (long double VALUE, int EXPONENT)
 -- Function: _FloatN ldexpfN (_FloatN VALUE, int EXPONENT)
 -- Function: _FloatNx ldexpfNx (_FloatNx VALUE, int EXPONENT)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the result of multiplying the floating-point
     number VALUE by 2 raised to the power EXPONENT.  (It can be used to
     reassemble floating-point numbers that were taken apart by
     ‘frexp’.)

     For example, ‘ldexp (0.8, 4)’ returns ‘12.8’.

   The following functions, which come from BSD, provide facilities
equivalent to those of ‘ldexp’ and ‘frexp’.  See also the ISO C function
‘logb’ which originally also appeared in BSD. The ‘_FloatN’ and
‘_FloatN’ variants of the following functions come from TS 18661-3:2015.

 -- Function: double scalb (double VALUE, double EXPONENT)
 -- Function: float scalbf (float VALUE, float EXPONENT)
 -- Function: long double scalbl (long double VALUE, long double
          EXPONENT)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘scalb’ function is the BSD name for ‘ldexp’.

 -- Function: double scalbn (double X, int N)
 -- Function: float scalbnf (float X, int N)
 -- Function: long double scalbnl (long double X, int N)
 -- Function: _FloatN scalbnfN (_FloatN X, int N)
 -- Function: _FloatNx scalbnfNx (_FloatNx X, int N)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘scalbn’ is identical to ‘scalb’, except that the exponent N is an
     ‘int’ instead of a floating-point number.

 -- Function: double scalbln (double X, long int N)
 -- Function: float scalblnf (float X, long int N)
 -- Function: long double scalblnl (long double X, long int N)
 -- Function: _FloatN scalblnfN (_FloatN X, long int N)
 -- Function: _FloatNx scalblnfNx (_FloatNx X, long int N)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘scalbln’ is identical to ‘scalb’, except that the exponent N is a
     ‘long int’ instead of a floating-point number.

 -- Function: double significand (double X)
 -- Function: float significandf (float X)
 -- Function: long double significandl (long double X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     ‘significand’ returns the mantissa of X scaled to the range [1, 2).
     It is equivalent to ‘scalb (X, (double) -ilogb (X))’.

     This function exists mainly for use in certain standardized tests
     of IEEE 754 conformance.


File: libc.info,  Node: Rounding Functions,  Next: Remainder Functions,  Prev: Normalization Functions,  Up: Arithmetic Functions

20.8.3 Rounding Functions
-------------------------

The functions listed here perform operations such as rounding and
truncation of floating-point values.  Some of these functions convert
floating point numbers to integer values.  They are all declared in
‘math.h’.

   You can also convert floating-point numbers to integers simply by
casting them to ‘int’.  This discards the fractional part, effectively
rounding towards zero.  However, this only works if the result can
actually be represented as an ‘int’—for very large numbers, this is
impossible.  The functions listed here return the result as a ‘double’
instead to get around this problem.

   The ‘fromfp’ functions use the following macros, from TS
18661-1:2014, to specify the direction of rounding.  These correspond to
the rounding directions defined in IEEE 754-2008.

‘FP_INT_UPWARD’

     Round toward +oo.

‘FP_INT_DOWNWARD’

     Round toward -oo.

‘FP_INT_TOWARDZERO’

     Round toward zero.

‘FP_INT_TONEARESTFROMZERO’

     Round to nearest, ties round away from zero.

‘FP_INT_TONEAREST’

     Round to nearest, ties round to even.

 -- Function: double ceil (double X)
 -- Function: float ceilf (float X)
 -- Function: long double ceill (long double X)
 -- Function: _FloatN ceilfN (_FloatN X)
 -- Function: _FloatNx ceilfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions round X upwards to the nearest integer, returning
     that value as a ‘double’.  Thus, ‘ceil (1.5)’ is ‘2.0’.

 -- Function: double floor (double X)
 -- Function: float floorf (float X)
 -- Function: long double floorl (long double X)
 -- Function: _FloatN floorfN (_FloatN X)
 -- Function: _FloatNx floorfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions round X downwards to the nearest integer, returning
     that value as a ‘double’.  Thus, ‘floor (1.5)’ is ‘1.0’ and ‘floor
     (-1.5)’ is ‘-2.0’.

 -- Function: double trunc (double X)
 -- Function: float truncf (float X)
 -- Function: long double truncl (long double X)
 -- Function: _FloatN truncfN (_FloatN X)
 -- Function: _FloatNx truncfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘trunc’ functions round X towards zero to the nearest integer
     (returned in floating-point format).  Thus, ‘trunc (1.5)’ is ‘1.0’
     and ‘trunc (-1.5)’ is ‘-1.0’.

 -- Function: double rint (double X)
 -- Function: float rintf (float X)
 -- Function: long double rintl (long double X)
 -- Function: _FloatN rintfN (_FloatN X)
 -- Function: _FloatNx rintfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions round X to an integer value according to the
     current rounding mode.  *Note Floating Point Parameters::, for
     information about the various rounding modes.  The default rounding
     mode is to round to the nearest integer; some machines support
     other modes, but round-to-nearest is always used unless you
     explicitly select another.

     If X was not initially an integer, these functions raise the
     inexact exception.

 -- Function: double nearbyint (double X)
 -- Function: float nearbyintf (float X)
 -- Function: long double nearbyintl (long double X)
 -- Function: _FloatN nearbyintfN (_FloatN X)
 -- Function: _FloatNx nearbyintfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions return the same value as the ‘rint’ functions, but
     do not raise the inexact exception if X is not an integer.

 -- Function: double round (double X)
 -- Function: float roundf (float X)
 -- Function: long double roundl (long double X)
 -- Function: _FloatN roundfN (_FloatN X)
 -- Function: _FloatNx roundfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions are similar to ‘rint’, but they round halfway cases
     away from zero instead of to the nearest integer (or other current
     rounding mode).

 -- Function: double roundeven (double X)
 -- Function: float roundevenf (float X)
 -- Function: long double roundevenl (long double X)
 -- Function: _FloatN roundevenfN (_FloatN X)
 -- Function: _FloatNx roundevenfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions, from TS 18661-1:2014 and TS 18661-3:2015, are
     similar to ‘round’, but they round halfway cases to even instead of
     away from zero.

 -- Function: long int lrint (double X)
 -- Function: long int lrintf (float X)
 -- Function: long int lrintl (long double X)
 -- Function: long int lrintfN (_FloatN X)
 -- Function: long int lrintfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions are just like ‘rint’, but they return a ‘long int’
     instead of a floating-point number.

 -- Function: long long int llrint (double X)
 -- Function: long long int llrintf (float X)
 -- Function: long long int llrintl (long double X)
 -- Function: long long int llrintfN (_FloatN X)
 -- Function: long long int llrintfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions are just like ‘rint’, but they return a ‘long long
     int’ instead of a floating-point number.

 -- Function: long int lround (double X)
 -- Function: long int lroundf (float X)
 -- Function: long int lroundl (long double X)
 -- Function: long int lroundfN (_FloatN X)
 -- Function: long int lroundfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions are just like ‘round’, but they return a ‘long int’
     instead of a floating-point number.

 -- Function: long long int llround (double X)
 -- Function: long long int llroundf (float X)
 -- Function: long long int llroundl (long double X)
 -- Function: long long int llroundfN (_FloatN X)
 -- Function: long long int llroundfNx (_FloatNx X)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions are just like ‘round’, but they return a ‘long long
     int’ instead of a floating-point number.

 -- Function: intmax_t fromfp (double X, int ROUND, unsigned int WIDTH)
 -- Function: intmax_t fromfpf (float X, int ROUND, unsigned int WIDTH)
 -- Function: intmax_t fromfpl (long double X, int ROUND, unsigned int
          WIDTH)
 -- Function: intmax_t fromfpfN (_FloatN X, int ROUND, unsigned int
          WIDTH)
 -- Function: intmax_t fromfpfNx (_FloatNx X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfp (double X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfpf (float X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfpl (long double X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfpfN (_FloatN X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfpfNx (_FloatNx X, int ROUND, unsigned int
          WIDTH)
 -- Function: intmax_t fromfpx (double X, int ROUND, unsigned int WIDTH)
 -- Function: intmax_t fromfpxf (float X, int ROUND, unsigned int WIDTH)
 -- Function: intmax_t fromfpxl (long double X, int ROUND, unsigned int
          WIDTH)
 -- Function: intmax_t fromfpxfN (_FloatN X, int ROUND, unsigned int
          WIDTH)
 -- Function: intmax_t fromfpxfNx (_FloatNx X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfpx (double X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfpxf (float X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfpxl (long double X, int ROUND, unsigned
          int WIDTH)
 -- Function: uintmax_t ufromfpxfN (_FloatN X, int ROUND, unsigned int
          WIDTH)
 -- Function: uintmax_t ufromfpxfNx (_FloatNx X, int ROUND, unsigned int
          WIDTH)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions, from TS 18661-1:2014 and TS 18661-3:2015, convert
     a floating-point number to an integer according to the rounding
     direction ROUND (one of the ‘FP_INT_*’ macros).  If the integer is
     outside the range of a signed or unsigned (depending on the return
     type of the function) type of width WIDTH bits (or outside the
     range of the return type, if WIDTH is larger), or if X is infinite
     or NaN, or if WIDTH is zero, a domain error occurs and an
     unspecified value is returned.  The functions with an ‘x’ in their
     names raise the inexact exception when a domain error does not
     occur and the argument is not an integer; the other functions do
     not raise the inexact exception.

 -- Function: double modf (double VALUE, double *INTEGER-PART)
 -- Function: float modff (float VALUE, float *INTEGER-PART)
 -- Function: long double modfl (long double VALUE, long double
          *INTEGER-PART)
 -- Function: _FloatN modffN (_FloatN VALUE, _FloatN *INTEGER-PART)
 -- Function: _FloatNx modffNx (_FloatNx VALUE, _FloatNx *INTEGER-PART)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     These functions break the argument VALUE into an integer part and a
     fractional part (between ‘-1’ and ‘1’, exclusive).  Their sum
     equals VALUE.  Each of the parts has the same sign as VALUE, and
     the integer part is always rounded toward zero.

     ‘modf’ stores the integer part in ‘*INTEGER-PART’, and returns the
     fractional part.  For example, ‘modf (2.5, &intpart)’ returns ‘0.5’
     and stores ‘2.0’ into ‘intpart’.

