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