Linux manual pages Section 3: Subroutines  

Name

signbit — test sign of a real floating-point number

Synopsis

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

Link with −lm.

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

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 appendix with recommended functions in IEEE 754/IEEE 854).

SEE ALSO

copysign(3)

COLOPHON

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