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():
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

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
 | Thread safety | MT-Safe

CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C99. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

SEE ALSO
copysign(3)

COLOPHON
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