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
   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 
   

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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