ilogb(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | BUGS | SEE ALSO | COLOPHON

ILOGB(3)                Linux Programmer's Manual               ILOGB(3)

NAME         top

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

SYNOPSIS         top

       #include <math.h>

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

       Link with -lm.

   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         top

       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         top

       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         top

       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         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │Interface                             Attribute     Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │ilogb(), ilogbf(), ilogbl()           │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO         top

       C99, POSIX.1-2001, POSIX.1-2008.

BUGS         top

       Before version 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         top

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

COLOPHON         top

       This page is part of release 5.11 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

                               2021-03-22                       ILOGB(3)

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