SIGNBIT

Section: Linux Programmer's Manual (3)
Updated: 2008-08-05
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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; or cc -std=c99

DESCRIPTION

signbit() is a generic macro which can work on all real floating-point types. It returns a non-zero 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 non-zero value.

NaNs and infinities have a sign bit.

RETURN VALUE

The signbit() macro returns non-zero if the sign of x is negative; otherwise it returns zero.

ERRORS

No errors occur.

CONFORMING TO

C99, POSIX.1-2001. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

COLOPHON

This page is part of release 3.22 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/.