File Coverage

src/int/i31_decred.c

Criterion	Covered	Total	%
statement	28	33	84.8
branch	7	10	70.0
condition			n/a
subroutine			n/a
pod			n/a
total	35	43	81.4

line	stmt	bran	code
1			/*
2			* Copyright (c) 2016 Thomas Pornin
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			void
29	124		br_i31_decode_reduce(uint32_t *x,
30			const void src, size_t len, const uint32_t m)
31			{
32			uint32_t m_ebitlen, m_rbitlen;
33			size_t mblen, k;
34			const unsigned char *buf;
35			uint32_t acc;
36			int acc_len;
37
38			/*
39			* Get the encoded bit length.
40			*/
41	124		m_ebitlen = m[0];
42
43			/*
44			* Special case for an invalid (null) modulus.
45			*/
46	124	50	if (m_ebitlen == 0) {
47	0		x[0] = 0;
48	0		return;
49			}
50
51			/*
52			* Clear the destination.
53			*/
54	124		br_i31_zero(x, m_ebitlen);
55
56			/*
57			* First decode directly as many bytes as possible. This requires
58			* computing the actual bit length.
59			*/
60	124		m_rbitlen = m_ebitlen >> 5;
61	124		m_rbitlen = (m_ebitlen & 31) + (m_rbitlen << 5) - m_rbitlen;
62	124		mblen = (m_rbitlen + 7) >> 3;
63	124		k = mblen - 1;
64	124	50	if (k >= len) {
65	0		br_i31_decode(x, src, len);
66	0		x[0] = m_ebitlen;
67	0		return;
68			}
69	124		buf = src;
70	124		br_i31_decode(x, buf, k);
71	124		x[0] = m_ebitlen;
72
73			/*
74			* Input remaining bytes, using 31-bit words.
75			*/
76	124		acc = 0;
77	124		acc_len = 0;
78	22840	100	while (k < len) {
79			uint32_t v;
80
81	22716		v = buf[k ++];
82	22716	100	if (acc_len >= 23) {
83	5765		acc_len -= 23;
84	5765		acc <<= (8 - acc_len);
85	5765		acc \|= v >> acc_len;
86	5765		br_i31_muladd_small(x, acc, m);
87	5765		acc = v & (0xFF >> (8 - acc_len));
88			} else {
89	16951		acc = (acc << 8) \| v;
90	16951		acc_len += 8;
91			}
92			}
93
94			/*
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.
97			*/
98	124	50	if (acc_len != 0) {
99	124		acc = (acc \| (x[1] << acc_len)) & 0x7FFFFFFF;
100	124		br_i31_rshift(x, 31 - acc_len);
101	124		br_i31_muladd_small(x, acc, m);
102			}
103			}