Added generic API for date range validation (with callbacks).
[BearSSL] / int / i31_fmont.c
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_i31_from_monty(uint32_t *x, const uint32_t *m, uint32_t m0i)
30 {
31 size_t len, u, v;
32
33 len = (m[0] + 31) >> 5;
34 for (u = 0; u < len; u ++) {
35 uint32_t f;
36 uint64_t cc;
37
38 f = MUL31_lo(x[1], m0i);
39 cc = 0;
40 for (v = 0; v < len; v ++) {
41 uint64_t z;
42
43 z = (uint64_t)x[v + 1] + MUL31(f, m[v + 1]) + cc;
44 cc = z >> 31;
45 if (v != 0) {
46 x[v] = (uint32_t)z & 0x7FFFFFFF;
47 }
48 }
49 x[len] = (uint32_t)cc;
50 }
51
52 /*
53 * We may have to do an extra subtraction, but only if the
54 * value in x[] is indeed greater than or equal to that of m[],
55 * which is why we must do two calls (first call computes the
56 * carry, second call performs the subtraction only if the carry
57 * is 0).
58 */
59 br_i31_sub(x, m, NOT(br_i31_sub(x, m, 0)));
60 }