SIGNBIT(3)                                          Linux Programmer's Manual                                         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(): _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 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.

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
       This page is part of release 3.25 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/.



GNU                                                        2008-08-05                                                 SIGNBIT(3)