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



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

SYNOPSIS
       #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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
       ilogbf(), ilogbl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 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 inte-
       ger.

       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 |
       +----------------------------+---------------+---------+
CONFORMING TO
       C99, POSIX.1-2001, POSIX.1-2008.

BUGS
       Before version 2.16, the following bugs existed in the glibc  implemen-
       tation 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 release 4.16 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/.



                                  2017-09-15                          ILOGB(3)