signbit(3)

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).

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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