NAME

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

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       int ilogb(double x);
       int ilogbf(float x);
       int ilogbl(long double x);

   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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       ilogbf(), ilogbl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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 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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C99, POSIX.1-2001.

BUGS

       Before  glibc  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)