SIGNBIT(3)                 Linux Programmer's Manual                SIGNBIT(3)



NAME
       signbit - test sign of a real floating-point number

SYNOPSIS
       #include <math.h>

       int signbit(x);

       Link with -lm.

   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  sign-
       bit(-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; oth-
       erwise 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 |
       +----------+---------------+---------+
CONFORMING TO
       POSIX.1-2001,  POSIX.1-2008,  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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GNU                               2017-09-15                        SIGNBIT(3)