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_encode(void *dst, size_t len, const uint32_t *x)
30  {
31  	unsigned char *buf;
32  	size_t k, xlen;
33  	uint32_t acc;
34  	int acc_len;
35  
36  	xlen = (x[0] + 31) >> 5;
37  	if (xlen == 0) {
38  		memset(dst, 0, len);
39  		return;
40  	}
41  	buf = (unsigned char *)dst + len;
42  	k = 1;
43  	acc = 0;
44  	acc_len = 0;
45  	while (len != 0) {
46  		uint32_t w;
47  
48  		w = (k <= xlen) ? x[k] : 0;
49  		k ++;
50  		if (acc_len == 0) {
51  			acc = w;
52  			acc_len = 31;
53  		} else {
54  			uint32_t z;
55  
56  			z = acc | (w << acc_len);
57  			acc_len --;
58  			acc = w >> (31 - acc_len);
59  			if (len >= 4) {
60  				buf -= 4;
61  				len -= 4;
62  				br_enc32be(buf, z);
63  			} else {
64  				switch (len) {
65  				case 3:
66  					buf[-3] = (unsigned char)(z >> 16);
67  					/* fall through */
68  				case 2:
69  					buf[-2] = (unsigned char)(z >> 8);
70  					/* fall through */
71  				case 1:
72  					buf[-1] = (unsigned char)z;
73  					break;
74  				}
75  				return;
76  			}
77  		}
78  	}
79  }