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 void
br_i32_decode_reduce(uint32_t * x,const void * src,size_t len,const uint32_t * m)29*0957b409SSimon J. Gerraty br_i32_decode_reduce(uint32_t *x,
30*0957b409SSimon J. Gerraty const void *src, size_t len, const uint32_t *m)
31*0957b409SSimon J. Gerraty {
32*0957b409SSimon J. Gerraty uint32_t m_bitlen;
33*0957b409SSimon J. Gerraty size_t mblen, k, q;
34*0957b409SSimon J. Gerraty const unsigned char *buf;
35*0957b409SSimon J. Gerraty
36*0957b409SSimon J. Gerraty m_bitlen = m[0];
37*0957b409SSimon J. Gerraty
38*0957b409SSimon J. Gerraty /*
39*0957b409SSimon J. Gerraty * Special case for an invalid modulus.
40*0957b409SSimon J. Gerraty */
41*0957b409SSimon J. Gerraty if (m_bitlen == 0) {
42*0957b409SSimon J. Gerraty x[0] = 0;
43*0957b409SSimon J. Gerraty return;
44*0957b409SSimon J. Gerraty }
45*0957b409SSimon J. Gerraty
46*0957b409SSimon J. Gerraty /*
47*0957b409SSimon J. Gerraty * Clear the destination.
48*0957b409SSimon J. Gerraty */
49*0957b409SSimon J. Gerraty br_i32_zero(x, m_bitlen);
50*0957b409SSimon J. Gerraty
51*0957b409SSimon J. Gerraty /*
52*0957b409SSimon J. Gerraty * First decode directly as many bytes as possible without
53*0957b409SSimon J. Gerraty * reduction, taking care to leave a number of bytes which
54*0957b409SSimon J. Gerraty * is a multiple of 4.
55*0957b409SSimon J. Gerraty */
56*0957b409SSimon J. Gerraty mblen = (m_bitlen + 7) >> 3;
57*0957b409SSimon J. Gerraty k = mblen - 1;
58*0957b409SSimon J. Gerraty
59*0957b409SSimon J. Gerraty /*
60*0957b409SSimon J. Gerraty * Up to k bytes can be safely decoded.
61*0957b409SSimon J. Gerraty */
62*0957b409SSimon J. Gerraty if (k >= len) {
63*0957b409SSimon J. Gerraty br_i32_decode(x, src, len);
64*0957b409SSimon J. Gerraty x[0] = m_bitlen;
65*0957b409SSimon J. Gerraty return;
66*0957b409SSimon J. Gerraty }
67*0957b409SSimon J. Gerraty
68*0957b409SSimon J. Gerraty /*
69*0957b409SSimon J. Gerraty * We want to first inject some bytes with direct decoding,
70*0957b409SSimon J. Gerraty * then extra bytes by whole 32-bit words. First compute
71*0957b409SSimon J. Gerraty * the size that should be injected that way.
72*0957b409SSimon J. Gerraty */
73*0957b409SSimon J. Gerraty buf = src;
74*0957b409SSimon J. Gerraty q = (len - k + 3) & ~(size_t)3;
75*0957b409SSimon J. Gerraty
76*0957b409SSimon J. Gerraty /*
77*0957b409SSimon J. Gerraty * It may happen that this is more than what we already have
78*0957b409SSimon J. Gerraty * (by at most 3 bytes). Such a case may happen only with
79*0957b409SSimon J. Gerraty * a very short modulus. In that case, we must process the first
80*0957b409SSimon J. Gerraty * bytes "manually".
81*0957b409SSimon J. Gerraty */
82*0957b409SSimon J. Gerraty if (q > len) {
83*0957b409SSimon J. Gerraty int i;
84*0957b409SSimon J. Gerraty uint32_t w;
85*0957b409SSimon J. Gerraty
86*0957b409SSimon J. Gerraty w = 0;
87*0957b409SSimon J. Gerraty for (i = 0; i < 4; i ++) {
88*0957b409SSimon J. Gerraty w <<= 8;
89*0957b409SSimon J. Gerraty if (q <= len) {
90*0957b409SSimon J. Gerraty w |= buf[len - q];
91*0957b409SSimon J. Gerraty }
92*0957b409SSimon J. Gerraty q --;
93*0957b409SSimon J. Gerraty }
94*0957b409SSimon J. Gerraty br_i32_muladd_small(x, w, m);
95*0957b409SSimon J. Gerraty } else {
96*0957b409SSimon J. Gerraty br_i32_decode(x, buf, len - q);
97*0957b409SSimon J. Gerraty x[0] = m_bitlen;
98*0957b409SSimon J. Gerraty }
99*0957b409SSimon J. Gerraty
100*0957b409SSimon J. Gerraty /*
101*0957b409SSimon J. Gerraty * At that point, we have exactly q bytes to inject, and q is
102*0957b409SSimon J. Gerraty * a multiple of 4.
103*0957b409SSimon J. Gerraty */
104*0957b409SSimon J. Gerraty for (k = len - q; k < len; k += 4) {
105*0957b409SSimon J. Gerraty br_i32_muladd_small(x, br_dec32be(buf + k), m);
106*0957b409SSimon J. Gerraty }
107*0957b409SSimon J. Gerraty }
108