SIGNBIT(3) Linux Programmer's Manual SIGNBIT(3)NAME
signbit - test sign of a real floating-point number
SYNOPSIS
#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
DESCRIPTIONsignbit() 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 sign‐
bit(-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; oth‐
erwise it returns zero.
ERRORS
No errors occur.
ATTRIBUTES
Multithreading (see pthreads(7))
The signbit() macro is thread-safe.
CONFORMING TO
C99, POSIX.1-2001. This function is defined in IEC 559 (and the appen‐
dix with recommended functions in IEEE 754/IEEE 854).
SEE ALSOcopysign(3)COLOPHON
This page is part of release 3.55 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2013-07-04 SIGNBIT(3)
