signbit (3)
Leading comments
Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpages@gmail.com>
%%%LICENSE_START(GPL_NOVERSION_ONELINE)
Distributed under GPL
%%%LICENSE_END
Based on glibc infopages, copyright Free Software Foundation
NAME
signbit - test sign of a real floating-point numberSYNOPSIS
#include <math.h>int signbit(x);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
signbit():
-
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTION
signbit() is a generic macro which can work on all real floating-point types. It returns a nonzero value if the value of x has its sign bit set.
This is not the same as
x < 0.0,
because IEEE 754 floating point allows zero to be signed.
The comparison
-0.0 < 0.0
is false, but
signbit(-0.0)
will return a nonzero value.
NaNs and infinities have a sign bit.
RETURN VALUE
The signbit() macro returns nonzero if the sign of x is negative; otherwise it returns zero.ERRORS
No errors occur.ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| signbit() | Thread safety | MT-Safe |