xref: /freebsd/contrib/bearssl/src/int/i32_decmod.c (revision 2aaf9152a852aba9eb2036b95f4948ee77988826)
1*0957b409SSimon J. Gerraty /*
2*0957b409SSimon J. Gerraty  * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
3*0957b409SSimon J. Gerraty  *
4*0957b409SSimon J. Gerraty  * Permission is hereby granted, free of charge, to any person obtaining
5*0957b409SSimon J. Gerraty  * a copy of this software and associated documentation files (the
6*0957b409SSimon J. Gerraty  * "Software"), to deal in the Software without restriction, including
7*0957b409SSimon J. Gerraty  * without limitation the rights to use, copy, modify, merge, publish,
8*0957b409SSimon J. Gerraty  * distribute, sublicense, and/or sell copies of the Software, and to
9*0957b409SSimon J. Gerraty  * permit persons to whom the Software is furnished to do so, subject to
10*0957b409SSimon J. Gerraty  * the following conditions:
11*0957b409SSimon J. Gerraty  *
12*0957b409SSimon J. Gerraty  * The above copyright notice and this permission notice shall be
13*0957b409SSimon J. Gerraty  * included in all copies or substantial portions of the Software.
14*0957b409SSimon J. Gerraty  *
15*0957b409SSimon J. Gerraty  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16*0957b409SSimon J. Gerraty  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17*0957b409SSimon J. Gerraty  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18*0957b409SSimon J. Gerraty  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19*0957b409SSimon J. Gerraty  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20*0957b409SSimon J. Gerraty  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21*0957b409SSimon J. Gerraty  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22*0957b409SSimon J. Gerraty  * SOFTWARE.
23*0957b409SSimon J. Gerraty  */
24*0957b409SSimon J. Gerraty 
25*0957b409SSimon J. Gerraty #include "inner.h"
26*0957b409SSimon J. Gerraty 
27*0957b409SSimon J. Gerraty /* see inner.h */
28*0957b409SSimon J. Gerraty uint32_t
br_i32_decode_mod(uint32_t * x,const void * src,size_t len,const uint32_t * m)29*0957b409SSimon J. Gerraty br_i32_decode_mod(uint32_t *x, const void *src, size_t len, const uint32_t *m)
30*0957b409SSimon J. Gerraty {
31*0957b409SSimon J. Gerraty 	const unsigned char *buf;
32*0957b409SSimon J. Gerraty 	uint32_t r;
33*0957b409SSimon J. Gerraty 	size_t u, v, mlen;
34*0957b409SSimon J. Gerraty 
35*0957b409SSimon J. Gerraty 	buf = src;
36*0957b409SSimon J. Gerraty 
37*0957b409SSimon J. Gerraty 	/*
38*0957b409SSimon J. Gerraty 	 * First pass: determine whether the value fits. The 'r' value
39*0957b409SSimon J. Gerraty 	 * will contain the comparison result, as 0x00000000 (value is
40*0957b409SSimon J. Gerraty 	 * equal to the modulus), 0x00000001 (value is greater than the
41*0957b409SSimon J. Gerraty 	 * modulus), or 0xFFFFFFFF (value is lower than the modulus).
42*0957b409SSimon J. Gerraty 	 */
43*0957b409SSimon J. Gerraty 	mlen = (m[0] + 7) >> 3;
44*0957b409SSimon J. Gerraty 	r = 0;
45*0957b409SSimon J. Gerraty 	for (u = (mlen > len) ? mlen : len; u > 0; u --) {
46*0957b409SSimon J. Gerraty 		uint32_t mb, xb;
47*0957b409SSimon J. Gerraty 
48*0957b409SSimon J. Gerraty 		v = u - 1;
49*0957b409SSimon J. Gerraty 		if (v >= mlen) {
50*0957b409SSimon J. Gerraty 			mb = 0;
51*0957b409SSimon J. Gerraty 		} else {
52*0957b409SSimon J. Gerraty 			mb = (m[1 + (v >> 2)] >> ((v & 3) << 3)) & 0xFF;
53*0957b409SSimon J. Gerraty 		}
54*0957b409SSimon J. Gerraty 		if (v >= len) {
55*0957b409SSimon J. Gerraty 			xb = 0;
56*0957b409SSimon J. Gerraty 		} else {
57*0957b409SSimon J. Gerraty 			xb = buf[len - u];
58*0957b409SSimon J. Gerraty 		}
59*0957b409SSimon J. Gerraty 		r = MUX(EQ(r, 0), (uint32_t)CMP(xb, mb), r);
60*0957b409SSimon J. Gerraty 	}
61*0957b409SSimon J. Gerraty 
62*0957b409SSimon J. Gerraty 	/*
63*0957b409SSimon J. Gerraty 	 * Only r == 0xFFFFFFFF is acceptable. We want to set r to 0xFF if
64*0957b409SSimon J. Gerraty 	 * the value fits, 0x00 otherwise.
65*0957b409SSimon J. Gerraty 	 */
66*0957b409SSimon J. Gerraty 	r >>= 24;
67*0957b409SSimon J. Gerraty 	br_i32_zero(x, m[0]);
68*0957b409SSimon J. Gerraty 	u = (mlen > len) ? len : mlen;
69*0957b409SSimon J. Gerraty 	while (u > 0) {
70*0957b409SSimon J. Gerraty 		uint32_t xb;
71*0957b409SSimon J. Gerraty 
72*0957b409SSimon J. Gerraty 		xb = buf[len - u] & r;
73*0957b409SSimon J. Gerraty 		u --;
74*0957b409SSimon J. Gerraty 		x[1 + (u >> 2)] |= xb << ((u & 3) << 3);
75*0957b409SSimon J. Gerraty 	}
76*0957b409SSimon J. Gerraty 	return r >> 7;
77*0957b409SSimon J. Gerraty }
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