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
29  br_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  }