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)