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ILOGB
Section: Linux Programmer's Manual (3)
Updated: 20150419
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NAME
ilogb, ilogbf, ilogbl  get integer exponent of a floatingpoint 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 floatingpoint exception
(FE_INVALID)
is raised, and
errno
is set to
EDOM
(but see BUGS).

 Domain error: x is an infinity

An invalid floatingpoint 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  MTSafe

CONFORMING TO
C99, POSIX.12001, POSIX.12008.
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 floatingpoint exception.
 *

The domain error case where
x
is an infinity did not cause
errno
to be set or raise a floatingpoint exception.
SEE ALSO
log(3),
logb(3),
significand(3)
COLOPHON
This page is part of release 4.04 of the Linux
manpages
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/manpages/.
Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUE

 ERRORS

 ATTRIBUTES

 CONFORMING TO

 BUGS

 SEE ALSO

 COLOPHON

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