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  uint32_t
29  br_i32_decode_mod(uint32_t *x, const void *src, size_t len, const uint32_t *m)
30  {
31  	const unsigned char *buf;
32  	uint32_t r;
33  	size_t u, v, mlen;
34  
35  	buf = src;
36  
37  	/*
38  	 * First pass: determine whether the value fits. The 'r' value
39  	 * will contain the comparison result, as 0x00000000 (value is
40  	 * equal to the modulus), 0x00000001 (value is greater than the
41  	 * modulus), or 0xFFFFFFFF (value is lower than the modulus).
42  	 */
43  	mlen = (m[0] + 7) >> 3;
44  	r = 0;
45  	for (u = (mlen > len) ? mlen : len; u > 0; u --) {
46  		uint32_t mb, xb;
47  
48  		v = u - 1;
49  		if (v >= mlen) {
50  			mb = 0;
51  		} else {
52  			mb = (m[1 + (v >> 2)] >> ((v & 3) << 3)) & 0xFF;
53  		}
54  		if (v >= len) {
55  			xb = 0;
56  		} else {
57  			xb = buf[len - u];
58  		}
59  		r = MUX(EQ(r, 0), (uint32_t)CMP(xb, mb), r);
60  	}
61  
62  	/*
63  	 * Only r == 0xFFFFFFFF is acceptable. We want to set r to 0xFF if
64  	 * the value fits, 0x00 otherwise.
65  	 */
66  	r >>= 24;
67  	br_i32_zero(x, m[0]);
68  	u = (mlen > len) ? len : mlen;
69  	while (u > 0) {
70  		uint32_t xb;
71  
72  		xb = buf[len - u] & r;
73  		u --;
74  		x[1 + (u >> 2)] |= xb << ((u & 3) << 3);
75  	}
76  	return r >> 7;
77  }