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

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GNU                                                2017-09-15                                         SIGNBIT(3)