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Linux 2.6 - man page for signbit (linux section 3)

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 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
       This  page  is  part of release 3.55 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					    2013-07-04				       SIGNBIT(3)


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