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.

              These functions do not set errno for this case.

       Domain error: x is an infinity

              These functions do not set errno or raise an exception for this case.

ATTRIBUTES

   Multithreading (see pthreads(7))
       The ilogb(), ilogbf(), and ilogbl() functions are thread-safe.

CONFORMING TO

       C99, POSIX.1-2001.

SEE ALSO

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

COLOPHON

       This  page  is  part  of  release 3.54 of the Linux man-pages project.  A description of the project, and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

                                                   2013-08-06                                           ILOGB(3)