signbit(3) — Linux manual page

signbit(3)              Library Functions Manual              signbit(3)

NAME         top

       signbit - test sign of a real floating-point number

LIBRARY         top

       Math library (libm, -lm)

SYNOPSIS         top

       #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         top

       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         top

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

ERRORS         top

       No errors occur.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │Interface                             │ Attribute     │ Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │signbit()                             │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

       POSIX.1-2001, C99.

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

SEE ALSO         top

       copysign(3)

Linux man-pages 6.04           2023-03-30                     signbit(3)

Pages that refer to this page: copysign(3),  fpclassify(3)

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