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);
 
[Note] Note
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 versions <= 2.19:
*/ _BSD_SOURCE || _SVID_SOURCE
ilogbf(), ilogbl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
*/ _BSD_SOURCE || _SVID_SOURCE
[Note] Note

Link with −lm.

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

This page is part of release 4.07 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 https://www.kernel.org/doc/man−pages/.


  Copyright 2004 Andries Brouwer <aebcwi.nl>.
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
    <mtk.manpagesgmail.com>

%%%LICENSE_START(VERBATIM)
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
%%%LICENSE_END

Inspired by a page by Walter Harms created 2002-08-10