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():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
           _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99
       ilogbf(), ilogbl():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
           _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99

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 │
       └────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

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

BUGS

       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

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

COLOPHON

       This  page  is  part of release 4.04 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 http://www.kernel.org/doc/man-pages/.

                                            2015-04-19                                   ILOGB(3)