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      1 /*	$NetBSD: s_nan.c,v 1.2 2013/02/09 20:19:13 christos Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2007 David Schultz
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     19  * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
     20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     26  * SUCH DAMAGE.
     27  *
     28  * $FreeBSD: src/lib/msun/src/s_nan.c,v 1.2 2007/12/18 23:46:32 das Exp $
     29  */
     30 #include <sys/cdefs.h>
     31 __RCSID("$NetBSD: s_nan.c,v 1.2 2013/02/09 20:19:13 christos Exp $");
     32 
     33 #include <sys/endian.h>
     34 #include <ctype.h>
     35 #include <float.h>
     36 #include <math.h>
     37 #include <stdint.h>
     38 #include <string.h>
     39 
     40 #include "math_private.h"
     41 
     42 /* XXX: Locale? not here? in <ctype.h>? */
     43 static int
     44 digittoint(char s) {
     45 	if (isdigit((unsigned char)s))
     46 		return s - '0';
     47 	if (islower((unsigned char)s))
     48 		return s - 'a' + 10;
     49 	return s - 'A' + 10;
     50 }
     51 
     52 /*
     53  * Scan a string of hexadecimal digits (the format nan(3) expects) and
     54  * make a bit array (using the local endianness). We stop when we
     55  * encounter an invalid character, NUL, etc.  If we overflow, we do
     56  * the same as gcc's __builtin_nan(), namely, discard the high order bits.
     57  *
     58  * The format this routine accepts needs to be compatible with what is used
     59  * in contrib/gdtoa/hexnan.c (for strtod/scanf) and what is used in
     60  * __builtin_nan(). In fact, we're only 100% compatible for strings we
     61  * consider valid, so we might be violating the C standard. But it's
     62  * impossible to use nan(3) portably anyway, so this seems good enough.
     63  */
     64 static void
     65 _scan_nan(uint32_t *words, int num_words, const char *s)
     66 {
     67 	int si;		/* index into s */
     68 	int bitpos;	/* index into words (in bits) */
     69 
     70 	memset(words, 0, num_words * sizeof(*words));
     71 
     72 	/* Allow a leading '0x'. (It's expected, but redundant.) */
     73 	if (s[0] == '0' && (s[1] == 'x' || s[1] == 'X'))
     74 		s += 2;
     75 
     76 	/* Scan forwards in the string, looking for the end of the sequence. */
     77 	for (si = 0; isxdigit((unsigned char)s[si]); si++)
     78 		continue;
     79 
     80 	/* Scan backwards, filling in the bits in words[] as we go. */
     81 #if _BYTE_ORDER == _LITTLE_ENDIAN
     82 	for (bitpos = 0; bitpos < 32 * num_words; bitpos += 4) {
     83 #else
     84 	for (bitpos = 32 * num_words - 4; bitpos >= 0; bitpos -= 4) {
     85 #endif
     86 		if (--si < 0)
     87 			break;
     88 		words[bitpos / 32] |= digittoint(s[si]) << (bitpos % 32);
     89 	}
     90 }
     91 
     92 double
     93 nan(const char *s)
     94 {
     95 	union {
     96 		double d;
     97 		uint32_t bits[2];
     98 	} u;
     99 
    100 	_scan_nan(u.bits, 2, s);
    101 #if _BYTE_ORDER == _LITTLE_ENDIAN
    102 	u.bits[1] |= 0x7ff80000;
    103 #else
    104 	u.bits[0] |= 0x7ff80000;
    105 #endif
    106 	return (u.d);
    107 }
    108 
    109 float
    110 nanf(const char *s)
    111 {
    112 	union {
    113 		float f;
    114 		uint32_t bits[1];
    115 	} u;
    116 
    117 	_scan_nan(u.bits, 1, s);
    118 	u.bits[0] |= 0x7fc00000;
    119 	return (u.f);
    120 }
    121 
    122 #if (LDBL_MANT_DIG == 53)
    123 __weak_reference(nan, nanl);
    124 #endif
    125