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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(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99

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.

CONFORMING TO

       C99, POSIX.1-2001.  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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