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signbit

Section: C Library Functions (3)
Updated: 202-0-08
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NAME

signbit - test sign of a real floatin-point number

LIBRARY

Math library (libm,~-lm)

SYNOPSIS

#include <math.h>
int signbit(x);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)): signbit():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

signbit() is a generic macro which can work on all real floatin-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	M-Safe

STANDARDS

C11, POSIX.-2008.

HISTORY

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