Added generic API for date range validation (with callbacks).
[BearSSL] / int / i31_decred.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_decode_reduce(uint32_t *x,
30 const void *src, size_t len, const uint32_t *m)
31 {
32 uint32_t m_ebitlen, m_rbitlen;
33 size_t mblen, k;
34 const unsigned char *buf;
35 uint32_t acc;
36 int acc_len;
37
38 /*
39 * Get the encoded bit length.
40 */
41 m_ebitlen = m[0];
42
43 /*
44 * Special case for an invalid (null) modulus.
45 */
46 if (m_ebitlen == 0) {
47 x[0] = 0;
48 return;
49 }
50
51 /*
52 * Clear the destination.
53 */
54 br_i31_zero(x, m_ebitlen);
55
56 /*
57 * First decode directly as many bytes as possible. This requires
58 * computing the actual bit length.
59 */
60 m_rbitlen = m_ebitlen >> 5;
61 m_rbitlen = (m_ebitlen & 31) + (m_rbitlen << 5) - m_rbitlen;
62 mblen = (m_rbitlen + 7) >> 3;
63 k = mblen - 1;
64 if (k >= len) {
65 br_i31_decode(x, src, len);
66 x[0] = m_ebitlen;
67 return;
68 }
69 buf = src;
70 br_i31_decode(x, buf, k);
71 x[0] = m_ebitlen;
72
73 /*
74 * Input remaining bytes, using 31-bit words.
75 */
76 acc = 0;
77 acc_len = 0;
78 while (k < len) {
79 uint32_t v;
80
81 v = buf[k ++];
82 if (acc_len >= 23) {
83 acc_len -= 23;
84 acc <<= (8 - acc_len);
85 acc |= v >> acc_len;
86 br_i31_muladd_small(x, acc, m);
87 acc = v & (0xFF >> (8 - acc_len));
88 } else {
89 acc = (acc << 8) | v;
90 acc_len += 8;
91 }
92 }
93
94 /*
95 * We may have some bits accumulated. We then perform a shift to
96 * be able to inject these bits as a full 31-bit word.
97 */
98 if (acc_len != 0) {
99 acc = (acc | (x[1] << acc_len)) & 0x7FFFFFFF;
100 br_i31_rshift(x, 31 - acc_len);
101 br_i31_muladd_small(x, acc, m);
102 }
103 }