sysdeps/ieee754/bits/nan.h

   1 /* `NAN' constant for IEEE 754 machines.
   2    Copyright (C) 1992,1996,1997,1999,2004,2006 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    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 #if __GNUC_PREREQ(3,3)
  28
  29 # define NAN    (__builtin_nanf (""))
  30
  31 #elif defined __GNUC__
  32
  33 # define NAN \
  34   (__extension__                                                              \
  35    ((union { unsigned __l __attribute__ ((__mode__ (__SI__))); float __d; })  \
  36     { __l: 0x7fc00000UL }).__d)
  37
  38 #else
  39
  40 # include <endian.h>
  41
  42 # if __BYTE_ORDER == __BIG_ENDIAN
  43 #  define __nan_bytes           { 0x7f, 0xc0, 0, 0 }
  44 # endif
  45 # if __BYTE_ORDER == __LITTLE_ENDIAN
  46 #  define __nan_bytes           { 0, 0, 0xc0, 0x7f }
  47 # endif
  48
  49 static union { unsigned char __c[4]; float __d; } __nan_union
  50     __attribute_used__ = { __nan_bytes };
  51 # define NAN    (__nan_union.__d)
  52
  53 #endif  /* GCC.  */