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)

Linux man-pages 6.7                                2023-10-31                                         signbit(3)