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ilogb(3) — Linux manual page

ilogb(3)                 Library Functions Manualilogb(3)

NAME        top

       ilogb, ilogbf, ilogbl - get integer exponent of a floating-point       value

LIBRARY        top

       Math library (libm,-lm)

SYNOPSIS        top

#include <math.h>int ilogb(doublex);int ilogbf(floatx);int ilogbl(long doublex);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):ilogb():           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L               || _XOPEN_SOURCE >= 500               || /* Since glibc 2.19: */ _DEFAULT_SOURCE               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEilogbf(),ilogbl():           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L               || /* Since glibc 2.19: */ _DEFAULT_SOURCE               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION        top

       These functions return the exponent part of their argument as a       signed integer.  When no error occurs, these functions are       equivalent to the correspondinglogb(3) functions, cast toint.

RETURN VALUE        top

       On success, these functions return the exponent ofx, as a signed       integer.       Ifx is zero, then a domain error occurs, and the functions returnFP_ILOGB0.       Ifx is a NaN, then a domain error occurs, and the functions       returnFP_ILOGBNAN.       Ifx is negative infinity or positive infinity, then a domain       error occurs, and the functions returnINT_MAX.

ERRORS        top

       Seemath_error(7) for information on how to determine whether an       error has occurred when calling these functions.       The following errors can occur:       Domain error:x is 0 or a NaN              An invalid floating-point exception (FE_INVALID) is raised,              anderrno is set toEDOM(but see BUGS).       Domain error:x is an infinity              An invalid floating-point exception (FE_INVALID) is raised,              anderrno is set toEDOM(but see BUGS).

ATTRIBUTES        top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │ilogb(),ilogbf(),ilogbl()          │ Thread safety │ MT-Safe │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS        top

       C11, POSIX.1-2008.

HISTORY        top

       C99, POSIX.1-2001.

BUGS        top

       Before glibc 2.16, the following bugs existed in the glibc       implementation of these functions:       •  The domain error case wherex is 0 or a NaN did not causeerrno          to be set or (on some architectures) raise a floating-point          exception.       •  The domain error case wherex is an infinity did not causeerrno to be set or raise a floating-point exception.

SEE ALSO        top

log(3),logb(3),significand(3)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17ilogb(3)

Pages that refer to this page:logb(3), significand(3)

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