NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | SEE ALSO | COLOPHON

SIGNBIT(3)                Linux Programmer's Manual               SIGNBIT(3)

NAME         top

       signbit - test sign of a real floating-point number

SYNOPSIS         top

       #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         top

       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         top

       The signbit() macro returns nonzero if the sign of x is negative;
       otherwise it returns zero.

ERRORS         top

       No errors occur.

ATTRIBUTES         top

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

       ┌──────────┬───────────────┬─────────┐
       │Interface Attribute     Value   │
       ├──────────┼───────────────┼─────────┤
       │signbit() │ Thread safety │ MT-Safe │
       └──────────┴───────────────┴─────────┘

CONFORMING TO         top

       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         top

       copysign(3)

COLOPHON         top

       This page is part of release 4.08 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/.

GNU                              2016-03-15                       SIGNBIT(3)