1 /* $NetBSD: fixunsgen_ieee754.c,v 1.4 2022/04/16 18:15:20 andvar Exp $ */
2
3 /*-
4 * Copyright (c) 1992, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This software was developed by the Computer Systems Engineering group
8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
9 * contributed to Berkeley.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
19 * 3. Neither the name of the University nor the names of its contributors
20 * may be used to endorse or promote products derived from this software
21 * without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35
36 #include <sys/cdefs.h>
37
38 #if !defined(FIXUNSNAME) && defined(LIBC_SCCS) && !defined(lint)
39 __RCSID("$NetBSD: fixunsgen_ieee754.c,v 1.4 2022/04/16 18:15:20 andvar Exp $");
40 #endif /* LIBC_SCCS and not lint */
41
42 #include <stddef.h>
43 #include <stdint.h>
44 #include <stdbool.h>
45 #include <float.h>
46
47 #ifndef FIXUNSNAME
48 #define FIXUNSNAME(n) n##32
49 #define UINTXX_T uint32_t
50 #endif
51
52 __dso_hidden UINTXX_T
53 FIXUNSNAME(__fixunsgen)(int, bool, size_t, size_t, const uint32_t *);
54
55 /*
56 * Convert double to (unsigned) int. All operations are done module 2^32.
57 */
58 UINTXX_T
FIXUNSNAME(__fixunsgen)59 FIXUNSNAME(__fixunsgen)(int exp, bool sign, size_t mant_dig, size_t fracbits,
60 const uint32_t *frac)
61 {
62 UINTXX_T tmp;
63
64 /*
65 * If it's less than 1 (negative exponent), it's going to round
66 * to zero. If the exponent is so large that it is a multiple of
67 * 2^N, then x module 2^N will be 0. (we use the fact treating a
68 * negative value as unsigned will be greater than nonnegative value)
69 */
70 if (__predict_false((size_t)exp >= mant_dig + sizeof(UINTXX_T)*8))
71 return 0;
72
73 /*
74 * This is simpler than it seems. Basically we are constructing
75 * fixed binary representation of the floating point number tossing
76 * away bits that wont be in the modulis we return.
77 */
78 tmp = 1;
79 for (size_t ebits = exp;;) {
80 if (ebits <= fracbits) {
81 /*
82 * The current fraction has more bits than we need.
83 * Shift the current value over and insert the bits
84 * we want. We're done.
85 */
86 tmp <<= (unsigned int)ebits;
87 tmp |= *frac >> (fracbits - ebits);
88 break;
89 }
90 if (fracbits == sizeof(tmp)*4) {
91 /*
92 * Shifts must be < sizeof(type). If it's going to be
93 * sizeof(type), just replace the value.
94 */
95 tmp = *frac--;
96 } else {
97 tmp <<= (unsigned int)fracbits;
98 tmp |= *frac--;
99 }
100 ebits -= fracbits;
101 fracbits = sizeof(frac[0]) * 4;
102 }
103
104 /*
105 * If the input was negative, make tmp negative module 2^32.
106 */
107 if (sign)
108 tmp = -tmp;
109
110 return tmp;
111 }
112