linux man page for signbit

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 || _POSIX_C_SOURCE >= 200112L;
	   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  sign-
       bit(-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 3.27 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
								    2010-09-20								SIGNBIT(3)