text: /*	$NetBSD: s_nan.c,v 1.2 2013/02/09 20:19:13 christos Exp $	*/
  
  /*-
   * Copyright (c) 2007 David Schultz
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * $FreeBSD: src/lib/msun/src/s_nan.c,v 1.2 2007/12/18 23:46:32 das Exp $
   */
  #include <sys/cdefs.h>
  __RCSID("$NetBSD: s_nan.c,v 1.2 2013/02/09 20:19:13 christos Exp $");
  
  #include <sys/endian.h>
  #include <ctype.h>
  #include <float.h>
  #include <math.h>
  #include <stdint.h>
  #include <string.h>
  
  #include "math_private.h"
  
  /* XXX: Locale? not here? in <ctype.h>? */
  static int
  digittoint(char s) {
  	if (isdigit((unsigned char)s))
  		return s - '0';
  	if (islower((unsigned char)s))
  		return s - 'a' + 10;
  	return s - 'A' + 10;
  }
  
  /*
   * Scan a string of hexadecimal digits (the format nan(3) expects) and
   * make a bit array (using the local endianness). We stop when we
   * encounter an invalid character, NUL, etc.  If we overflow, we do
   * the same as gcc's __builtin_nan(), namely, discard the high order bits.
   *
   * The format this routine accepts needs to be compatible with what is used
   * in contrib/gdtoa/hexnan.c (for strtod/scanf) and what is used in
   * __builtin_nan(). In fact, we're only 100% compatible for strings we
   * consider valid, so we might be violating the C standard. But it's
   * impossible to use nan(3) portably anyway, so this seems good enough.
   */
  static void
  _scan_nan(uint32_t *words, int num_words, const char *s)
  {
  	int si;		/* index into s */
  	int bitpos;	/* index into words (in bits) */
  
  	memset(words, 0, num_words * sizeof(*words));
  
  	/* Allow a leading '0x'. (It's expected, but redundant.) */
  	if (s[0] == '0' && (s[1] == 'x' || s[1] == 'X'))
  		s += 2;
  
  	/* Scan forwards in the string, looking for the end of the sequence. */
  	for (si = 0; isxdigit((unsigned char)s[si]); si++)
  		continue;
  
  	/* Scan backwards, filling in the bits in words[] as we go. */
  #if _BYTE_ORDER == _LITTLE_ENDIAN
  	for (bitpos = 0; bitpos < 32 * num_words; bitpos += 4) {
  #else
  	for (bitpos = 32 * num_words - 4; bitpos >= 0; bitpos -= 4) {
  #endif
  		if (--si < 0)
  			break;
  		words[bitpos / 32] |= digittoint(s[si]) << (bitpos % 32);
  	}
  }
  
  double
  nan(const char *s)
  {
  	union {
  		double d;
  		uint32_t bits[2];
  	} u;
  
  	_scan_nan(u.bits, 2, s);
  #if _BYTE_ORDER == _LITTLE_ENDIAN
  	u.bits[1] |= 0x7ff80000;
  #else
  	u.bits[0] |= 0x7ff80000;
  #endif
  	return (u.d);
  }
  
  float
  nanf(const char *s)
  {
  	union {
  		float f;
  		uint32_t bits[1];
  	} u;
  
  	_scan_nan(u.bits, 1, s);
  	u.bits[0] |= 0x7fc00000;
  	return (u.f);
  }
  
  #if (LDBL_MANT_DIG == 53)
  __weak_reference(nan, nanl);
  #endif
  