ilogb(3) — Linux manual page

ilogb(3)                Library Functions Manual                ilogb(3)

NAME

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

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       int ilogb(double x);
       int ilogbf(float x);
       int ilogbl(long double x);

   Feature Test Macro Requirements for glibc (see
   feature_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_SOURCE

       ilogbf(), ilogbl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

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

RETURN VALUE

       On success, these functions return the exponent of x, as a signed
       integer.

       If x is zero, then a domain error occurs, and the functions
       return FP_ILOGB0.

       If x is a NaN, then a domain error occurs, and the functions
       return FP_ILOGBNAN.

       If x is negative infinity or positive infinity, then a domain
       error occurs, and the functions return INT_MAX.

ERRORS

       See math_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, and errno is set to EDOM (but see BUGS).

       Domain error: x is an infinity
              An invalid floating-point exception (FE_INVALID) is
              raised, and errno is set to EDOM (but see BUGS).

ATTRIBUTES

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

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C99, POSIX.1-2001.

BUGS

       Before glibc 2.16, the following bugs existed in the glibc
       implementation of these functions:

       •  The domain error case where x is 0 or a NaN did not cause
          errno to be set or (on some architectures) raise a floating-
          point exception.

       •  The domain error case where x is an infinity did not cause
          errno to be set or raise a floating-point exception.

SEE ALSO

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

COLOPHON

       This page is part of the man-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-6.9.1.tar.gz
       fetched from
       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
       2024-06-26.  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 is not
       part of the original manual page), send a mail to
       man-pages@man7.org

Linux man-pages 6.9.1          2024-05-02                       ilogb(3)

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

---