signbit(3) — Linux manual page

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)

COLOPHON

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

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

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