signbit - test sign of a real floating-point number

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ signbit()                                                                   │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

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.

       No errors occur.

       POSIX.1-2001, C99.

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

       Math library (libm, -lm)

       signbit - test sign of a real floating-point number

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

copysign(3)

Linux man-pages 6.9.1                              2024-05-02                                         signbit(3)

       C11, POSIX.1-2008.

#include<math.h>intsignbit(x);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       signbit():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L