nan.h

Glibc 2.3.2源代码(解压后有100多M)

/* `NAN' constant for IEEE 754 machines.
   Copyright (C) 1992, 1996, 1997, 1999, 2002 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#ifndef _MATH_H
# error "Never use <bits/nan.h> directly; include <math.h> instead."
#endif


/* IEEE Not A Number (QNaN). Note that MIPS has the QNaN and SNaN patterns
   reversed compared to most other architectures. The IEEE spec left
   the definition of this open to implementations, and for MIPS the top
   bit of the mantissa must be SET to indicate a SNaN.  */

#ifdef	__GNUC__

# define NAN \
  (__extension__                                                            \
   ((union { unsigned __l __attribute__((__mode__(__SI__))); float __d; })  \
    { __l: 0x7fbfffffUL }).__d)

#else

# include <endian.h>

# if __BYTE_ORDER == __BIG_ENDIAN
#  define __nan_bytes		{ 0x7f, 0xbf, 0xff, 0xff }
# endif
# if __BYTE_ORDER == __LITTLE_ENDIAN
#  define __nan_bytes		{ 0xff, 0xff, 0xbf, 0x7f }
# endif

static union { unsigned char __c[4]; float __d; } __nan_union = { __nan_bytes };
# define NAN	(__nan_union.__d)

#endif	/* GCC.  */