.\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.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.\" manual page may be incorrect or out-of-date.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
.\"
.TH ILOGB 3 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
ilogb, ilogbf, ilogbl \- get integer exponent of a floating-point value
.SH SYNOPSIS
.B #include <math.h>
.PP
.BI "int ilogb(double " x );
.br
.BI "int ilogbf(float " x );
.br
.BI "int ilogbl(long double " x );
.PP
Link with \fI\-lm\fP.
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.ad l
.BR ilogb ():
.RS 4
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
    || _XOPEN_SOURCE\ >=\ 500
.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.br
.BR ilogbf (),
.BR ilogbl ():
.RS 4
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.ad b
.SH 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
.BR logb (3)
functions, cast to
.IR int .
.SH RETURN VALUE
On success, these functions return the exponent of
.IR x ,
as a signed integer.
.PP
If
.I x
is zero, then a domain error occurs, and the functions return
.\" the POSIX.1 spec for logb() says logb() gives pole error for this
.\" case, but for ilogb() it says domain error.
.BR FP_ILOGB0 .
.\" glibc: The numeric value is either `INT_MIN' or `-INT_MAX'.
.PP
If
.I x
is a NaN, then a domain error occurs, and the functions return
.BR FP_ILOGBNAN .
.\" glibc: The numeric value is either `INT_MIN' or `INT_MAX'.
.\" On i386, FP_ILOGB0 and FP_ILOGBNAN have the same value.
.PP
If
.I x
is negative infinity or positive infinity, then
a domain error occurs, and the functions return
.BR INT_MAX .
.\"
.\" POSIX.1-2001 also says:
.\" If the correct value is greater than {INT_MAX}, {INT_MAX}
.\" shall be returned and a domain error shall occur.
.\"
.\" If the correct value is less than {INT_MIN}, {INT_MIN}
.\" shall be returned and a domain error shall occur.
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.PP
The following errors can occur:
.TP
Domain error: \fIx\fP is 0 or a NaN
An invalid floating-point exception
.RB ( FE_INVALID )
is raised, and
.I errno
is set to
.BR EDOM
(but see BUGS).
.TP
Domain error: \fIx\fP is an infinity
An invalid floating-point exception
.RB ( FE_INVALID )
is raised, and
.I errno
is set to
.BR EDOM
(but see BUGS).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw27 lb lb
l l l.
Interface	Attribute	Value
T{
.BR ilogb (),
.BR ilogbf (),
.BR ilogbl ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
.SH BUGS
.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6794
Before version 2.16, the following bugs existed in the
glibc implementation of these functions:
.IP * 3
The domain error case where
.I x
is 0 or a NaN did not cause
.I errno
to be set or (on some architectures) raise a floating-point exception.
.IP * 3
The domain error case where
.I x
is an infinity did not cause
.I errno
to be set or raise a floating-point exception.
.SH SEE ALSO
.BR log (3),
.BR logb (3),
.BR significand (3)
.SH COLOPHON
This page is part of release 5.10 of the Linux
.I 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/.