NAME

       signbit - test sign of a real floating-point number

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       int signbit(x);

   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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       POSIX.1-2001, C99.

       This function is defined in IEC 559 (and the appendix with recommended functions  in  IEEE
       754/IEEE 854).

SEE ALSO

       copysign(3)