Added generic API for date range validation (with callbacks).
[BearSSL] / int / i15_reduce.c
1 /*
2 * Copyright (c) 2017 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_i15_reduce(uint16_t *x, const uint16_t *a, const uint16_t *m)
30 {
31 uint32_t m_bitlen, a_bitlen;
32 size_t mlen, alen, u;
33
34 m_bitlen = m[0];
35 mlen = (m_bitlen + 15) >> 4;
36
37 x[0] = m_bitlen;
38 if (m_bitlen == 0) {
39 return;
40 }
41
42 /*
43 * If the source is shorter, then simply copy all words from a[]
44 * and zero out the upper words.
45 */
46 a_bitlen = a[0];
47 alen = (a_bitlen + 15) >> 4;
48 if (a_bitlen < m_bitlen) {
49 memcpy(x + 1, a + 1, alen * sizeof *a);
50 for (u = alen; u < mlen; u ++) {
51 x[u + 1] = 0;
52 }
53 return;
54 }
55
56 /*
57 * The source length is at least equal to that of the modulus.
58 * We must thus copy N-1 words, and input the remaining words
59 * one by one.
60 */
61 memcpy(x + 1, a + 2 + (alen - mlen), (mlen - 1) * sizeof *a);
62 x[mlen] = 0;
63 for (u = 1 + alen - mlen; u > 0; u --) {
64 br_i15_muladd_small(x, a[u], m);
65 }
66 }