2 * Copyright (c) 2016 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_i31_decode_reduce(uint32_t *x
,
30 const void *src
, size_t len
, const uint32_t *m
)
32 uint32_t m_ebitlen
, m_rbitlen
;
34 const unsigned char *buf
;
39 * Get the encoded bit length.
44 * Special case for an invalid (null) modulus.
52 * Clear the destination.
54 br_i31_zero(x
, m_ebitlen
);
57 * First decode directly as many bytes as possible. This requires
58 * computing the actual bit length.
60 m_rbitlen
= m_ebitlen
>> 5;
61 m_rbitlen
= (m_ebitlen
& 31) + (m_rbitlen
<< 5) - m_rbitlen
;
62 mblen
= (m_rbitlen
+ 7) >> 3;
65 br_i31_decode(x
, src
, len
);
70 br_i31_decode(x
, buf
, k
);
74 * Input remaining bytes, using 31-bit words.
84 acc
<<= (8 - acc_len
);
86 br_i31_muladd_small(x
, acc
, m
);
87 acc
= v
& (0xFF >> (8 - acc_len
));
95 * We may have some bits accumulated. We then perform a shift to
96 * be able to inject these bits as a full 31-bit word.
99 acc
= (acc
| (x
[1] << acc_len
)) & 0x7FFFFFFF;
100 br_i31_rshift(x
, 31 - acc_len
);
101 br_i31_muladd_small(x
, acc
, m
);