sysdeps/ieee754/bits/nan.h

   1 /* `NAN' constant for IEEE 754 machines.
   2    Copyright (C) 1992-2014 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #ifndef _MATH_H
  20 # error "Never use <bits/nan.h> directly; include <math.h> instead."
  21 #endif
  22
  23
  24 /* IEEE Not A Number.  */
  25
  26 #if __GNUC_PREREQ(3,3)
  27
  28 # define NAN    (__builtin_nanf (""))
  29
  30 #elif defined __GNUC__
  31
  32 # define NAN \
  33   (__extension__                                                              \
  34    ((union { unsigned __l __attribute__ ((__mode__ (__SI__))); float __d; })  \
  35     { __l: 0x7fc00000UL }).__d)
  36
  37 #else
  38
  39 # include <endian.h>
  40
  41 # if __BYTE_ORDER == __BIG_ENDIAN
  42 #  define __qnan_bytes          { 0x7f, 0xc0, 0, 0 }
  43 # endif
  44 # if __BYTE_ORDER == __LITTLE_ENDIAN
  45 #  define __qnan_bytes          { 0, 0, 0xc0, 0x7f }
  46 # endif
  47
  48 static union { unsigned char __c[4]; float __d; } __qnan_union
  49   __attribute__ ((__unused__)) = { __qnan_bytes };
  50 # define NAN    (__qnan_union.__d)
  51
  52 #endif  /* GCC.  */