2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
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:
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
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
29 br_i15_decode_mod(uint16_t *x
, const void *src
, size_t len
, const uint16_t *m
)
32 * Two-pass algorithm: in the first pass, we determine whether the
33 * value fits; in the second pass, we do the actual write.
35 * During the first pass, 'r' contains the comparison result so
37 * 0x00000000 value is equal to the modulus
38 * 0x00000001 value is greater than the modulus
39 * 0xFFFFFFFF value is lower than the modulus
41 * Since we iterate starting with the least significant bytes (at
42 * the end of src[]), each new comparison overrides the previous
43 * except when the comparison yields 0 (equal).
45 * During the second pass, 'r' is either 0xFFFFFFFF (value fits)
46 * or 0x00000000 (value does not fit).
48 * We must iterate over all bytes of the source, _and_ possibly
49 * some extra virutal bytes (with value 0) so as to cover the
50 * complete modulus as well. We also add 4 such extra bytes beyond
51 * the modulus length because it then guarantees that no accumulated
52 * partial word remains to be processed.
54 const unsigned char *buf
;
60 mlen
= (m
[0] + 15) >> 4;
67 for (pass
= 0; pass
< 2; pass
++) {
75 for (u
= 0; u
< tlen
; u
++) {
83 acc
|= (b
<< acc_len
);
88 xw
= acc
& (uint32_t)0x7FFF;
90 acc
= b
>> (8 - acc_len
);
97 cc
= (uint32_t)CMP(xw
, m
[v
]);
98 r
= MUX(EQ(cc
, 0), r
, cc
);
102 r
= MUX(EQ(xw
, 0), r
, 1);
110 * When we reach this point at the end of the first pass:
111 * r is either 0, 1 or -1; we want to set r to 0 if it
112 * is equal to 0 or 1, and leave it to -1 otherwise.
114 * When we reach this point at the end of the second pass:
115 * r is either 0 or -1; we want to leave that value
116 * untouched. This is a subcase of the previous.
123 return r
& (uint32_t)1;