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():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

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

       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 5.05 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 https://www.kernel.org/doc/man-pages/.