signbit(3) - Linux manual page (original) (raw)

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)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **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)](../man3/copysign.3.html)

COLOPHON top

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Linux man-pages 6.10 2024-07-23 signbit(3)

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