Manual Reference Pages - ILOGB (3)
NAME
ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value
CONTENTS
Synopsis
Description
Return Value
Errors
Colophon
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.
These functions do not set
errno for this case.
Domain error: x is an infinity
These functions do not set
errno or raise an exception for this case.

CONFORMING TO
C99, POSIX.1-2001.
SEE ALSO
log (3),
logb (3),
significand (3)
COLOPHON
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