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 3.74 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.



GNU                                         2013-07-04                                 SIGNBIT(3)