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_montymul(uint32_t * d,const uint32_t * x,const uint32_t * y,const uint32_t * m,uint32_t m0i)29 br_i31_montymul(uint32_t *d, const uint32_t *x, const uint32_t *y,
30 const uint32_t *m, uint32_t m0i)
31 {
32 size_t len, len4, u, v;
33 uint64_t dh;
34
35 len = (m[0] + 31) >> 5;
36 len4 = len & ~(size_t)3;
37 br_i31_zero(d, m[0]);
38 dh = 0;
39 for (u = 0; u < len; u ++) {
40 uint32_t f, xu;
41 uint64_t r, zh;
42
43 xu = x[u + 1];
44 f = MUL31_lo((d[1] + MUL31_lo(x[u + 1], y[1])), m0i);
45
46 r = 0;
47 for (v = 0; v < len4; v += 4) {
48 uint64_t z;
49
50 z = (uint64_t)d[v + 1] + MUL31(xu, y[v + 1])
51 + MUL31(f, m[v + 1]) + r;
52 r = z >> 31;
53 d[v + 0] = (uint32_t)z & 0x7FFFFFFF;
54 z = (uint64_t)d[v + 2] + MUL31(xu, y[v + 2])
55 + MUL31(f, m[v + 2]) + r;
56 r = z >> 31;
57 d[v + 1] = (uint32_t)z & 0x7FFFFFFF;
58 z = (uint64_t)d[v + 3] + MUL31(xu, y[v + 3])
59 + MUL31(f, m[v + 3]) + r;
60 r = z >> 31;
61 d[v + 2] = (uint32_t)z & 0x7FFFFFFF;
62 z = (uint64_t)d[v + 4] + MUL31(xu, y[v + 4])
63 + MUL31(f, m[v + 4]) + r;
64 r = z >> 31;
65 d[v + 3] = (uint32_t)z & 0x7FFFFFFF;
66 }
67 for (; v < len; v ++) {
68 uint64_t z;
69
70 z = (uint64_t)d[v + 1] + MUL31(xu, y[v + 1])
71 + MUL31(f, m[v + 1]) + r;
72 r = z >> 31;
73 d[v] = (uint32_t)z & 0x7FFFFFFF;
74 }
75
76 zh = dh + r;
77 d[len] = (uint32_t)zh & 0x7FFFFFFF;
78 dh = zh >> 31;
79 }
80
81 /*
82 * We must write back the bit length because it was overwritten in
83 * the loop (not overwriting it would require a test in the loop,
84 * which would yield bigger and slower code).
85 */
86 d[0] = m[0];
87
88 /*
89 * d[] may still be greater than m[] at that point; notably, the
90 * 'dh' word may be non-zero.
91 */
92 br_i31_sub(d, m, NEQ(dh, 0) | NOT(br_i31_sub(d, m, 0)));
93 }
94