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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 3.53 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)