sysdeps/ieee754/bits/nan.h

   1 /* `NAN' constant for IEEE 754 machines.
   2    Copyright (C) 1992, 1996, 1997 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #ifndef _MATH_H
  21 # error "Never use <bits/nan.h> directly; include <math.h> instead."
  22 #endif
  23
  24
  25 /* IEEE Not A Number.  */
  26
  27 #ifdef  __GNUC__
  28
  29 # define NAN \
  30   (__extension__                                                            \
  31    ((union { unsigned __l __attribute__((__mode__(__SI__))); float __d; })  \
  32     { __l: 0x7fc00000UL }).__d)
  33
  34 #else
  35
  36 # include <endian.h>
  37
  38 # if __BYTE_ORDER == __BIG_ENDIAN
  39 #  define __nan_bytes           { 0x7f, 0xc0, 0, 0 }
  40 # endif
  41 # if __BYTE_ORDER == __LITTLE_ENDIAN
  42 #  define __nan_bytes           { 0, 0, 0xc0, 0x7f }
  43 # endif
  44
  45 static union { unsigned char __c[4]; float __d; } __nan = { __nan_bytes };
  46 # define NAN    (__nan.__d)
  47
  48 #endif  /* GCC.  */