New basic implementation of Curve25519 (generic i15 code, experimental).
[BearSSL] / src / int / i32_decode.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_i32_decode(uint32_t *x, const void *src, size_t len)
30 {
31 const unsigned char *buf;
32 size_t u, v;
33
34 buf = src;
35 u = len;
36 v = 1;
37 for (;;) {
38 if (u < 4) {
39 uint32_t w;
40
41 if (u < 2) {
42 if (u == 0) {
43 break;
44 } else {
45 w = buf[0];
46 }
47 } else {
48 if (u == 2) {
49 w = br_dec16be(buf);
50 } else {
51 w = ((uint32_t)buf[0] << 16)
52 | br_dec16be(buf + 1);
53 }
54 }
55 x[v ++] = w;
56 break;
57 } else {
58 u -= 4;
59 x[v ++] = br_dec32be(buf + u);
60 }
61 }
62 x[0] = br_i32_bit_length(x + 1, v - 1);
63 }