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

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       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)