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 */
28void
29br_i32_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, u, v;
33	uint64_t dh;
34
35	len = (m[0] + 31) >> 5;
36	br_i32_zero(d, m[0]);
37	dh = 0;
38	for (u = 0; u < len; u ++) {
39		uint32_t f, xu;
40		uint64_t r1, r2, zh;
41
42		xu = x[u + 1];
43		f = (d[1] + x[u + 1] * y[1]) * m0i;
44		r1 = 0;
45		r2 = 0;
46		for (v = 0; v < len; v ++) {
47			uint64_t z;
48			uint32_t t;
49
50			z = (uint64_t)d[v + 1] + MUL(xu, y[v + 1]) + r1;
51			r1 = z >> 32;
52			t = (uint32_t)z;
53			z = (uint64_t)t + MUL(f, m[v + 1]) + r2;
54			r2 = z >> 32;
55			if (v != 0) {
56				d[v] = (uint32_t)z;
57			}
58		}
59		zh = dh + r1 + r2;
60		d[len] = (uint32_t)zh;
61		dh = zh >> 32;
62	}
63
64	/*
65	 * d[] may still be greater than m[] at that point; notably, the
66	 * 'dh' word may be non-zero.
67	 */
68	br_i32_sub(d, m, NEQ(dh, 0) | NOT(br_i32_sub(d, m, 0)));
69}
70