xref: /minix3/lib/libm/src/s_nan.c (revision 84d9c625bfea59e274550651111ae9edfdc40fbd)
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
digittoint(char s)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
_scan_nan(uint32_t * words,int num_words,const char * s)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