ILOGB
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Index
Return to Main Contents
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);
Link with -lm.
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
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 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
|
|
- Running on 
-
:
: 