signbit man page on Hurd

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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;  oth‐
       erwise 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 appen‐
       dix 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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