File Coverage

src/int/i32_decred.c

Criterion	Covered	Total	%
statement	0	26	0.0
branch	0	12	0.0
condition			n/a
subroutine			n/a
pod			n/a
total	0	38	0.0

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