1 /*
2 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25 #include "inner.h"
26
27 /* see inner.h */
28 void
br_i31_mulacc(uint32_t * d,const uint32_t * a,const uint32_t * b)29 br_i31_mulacc(uint32_t *d, const uint32_t *a, const uint32_t *b)
30 {
31 size_t alen, blen, u;
32 uint32_t dl, dh;
33
34 alen = (a[0] + 31) >> 5;
35 blen = (b[0] + 31) >> 5;
36
37 /*
38 * We want to add the two bit lengths, but these are encoded,
39 * which requires some extra care.
40 */
41 dl = (a[0] & 31) + (b[0] & 31);
42 dh = (a[0] >> 5) + (b[0] >> 5);
43 d[0] = (dh << 5) + dl + (~(uint32_t)(dl - 31) >> 31);
44
45 for (u = 0; u < blen; u ++) {
46 uint32_t f;
47 size_t v;
48
49 /*
50 * Carry always fits on 31 bits; we want to keep it in a
51 * 32-bit register on 32-bit architectures (on a 64-bit
52 * architecture, cast down from 64 to 32 bits means
53 * clearing the high bits, which is not free; on a 32-bit
54 * architecture, the same operation really means ignoring
55 * the top register, which has negative or zero cost).
56 */
57 #if BR_64
58 uint64_t cc;
59 #else
60 uint32_t cc;
61 #endif
62
63 f = b[1 + u];
64 cc = 0;
65 for (v = 0; v < alen; v ++) {
66 uint64_t z;
67
68 z = (uint64_t)d[1 + u + v] + MUL31(f, a[1 + v]) + cc;
69 cc = z >> 31;
70 d[1 + u + v] = (uint32_t)z & 0x7FFFFFFF;
71 }
72 d[1 + u + alen] = (uint32_t)cc;
73 }
74 }
75