signbit(3)                 Library Functions Manual                 signbit(3)

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)