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():
           _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)

GNU                                                                            2021-03-22                                                                     SIGNBIT(3)