ILOGB(3) Linux Programmer's Manual ILOGB(3)

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

#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

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.

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.

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

An invalid floating-point exception (FE_INVALID) is raised, and errno is set to EDOM (but see BUGS).
An invalid floating-point exception (FE_INVALID) is raised, and errno is set to EDOM (but see BUGS).

see_pthreads(7))">)">Multithreading (see pthreads(7))

The ilogb(), ilogbf(), and ilogbl() functions are thread-safe.

C99, POSIX.1-2001.

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 achitectures) 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.

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

This page is part of release 3.78 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/.

2014-12-31

Different Versions of this Page: