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;  oth-
       erwise it returns zero.

ERRORS
       No errors occur.

ATTRIBUTES
       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       +----------+---------------+---------+
       |Interface | Attribute     | Value   |
       +----------+---------------+---------+
       |signbit() | Thread safety | MT-Safe |
       +----------+---------------+---------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, C99.  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 4.04 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                               2015-08-08                        SIGNBIT(3)
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