xref: /freebsd/contrib/bearssl/src/int/i31_decode.c (revision 5ca8e32633c4ffbbcd6762e5888b6a4ba0708c6c)
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(uint32_t *x, const void *src, size_t len)
30 {
31 	const unsigned char *buf;
32 	size_t u, v;
33 	uint32_t acc;
34 	int acc_len;
35 
36 	buf = src;
37 	u = len;
38 	v = 1;
39 	acc = 0;
40 	acc_len = 0;
41 	while (u -- > 0) {
42 		uint32_t b;
43 
44 		b = buf[u];
45 		acc |= (b << acc_len);
46 		acc_len += 8;
47 		if (acc_len >= 31) {
48 			x[v ++] = acc & (uint32_t)0x7FFFFFFF;
49 			acc_len -= 31;
50 			acc = b >> (8 - acc_len);
51 		}
52 	}
53 	if (acc_len != 0) {
54 		x[v ++] = acc;
55 	}
56 	x[0] = br_i31_bit_length(x + 1, v - 1);
57 }
58