File Coverage

src/int/i32_modpow.c
Criterion Covered Total %
statement 0 13 0.0
branch 0 2 0.0
condition n/a
subroutine n/a
pod n/a
total 0 15 0.0


line stmt bran cond sub pod time 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_modpow(uint32_t *x,
30             const unsigned char *e, size_t elen,
31             const uint32_t *m, uint32_t m0i, uint32_t *t1, uint32_t *t2)
32             {
33             size_t mlen;
34             uint32_t k;
35              
36             /*
37             * 'mlen' is the length of m[] expressed in bytes (including
38             * the "bit length" first field).
39             */
40 0           mlen = ((m[0] + 63) >> 5) * sizeof m[0];
41              
42             /*
43             * Throughout the algorithm:
44             * -- t1[] is in Montgomery representation; it contains x, x^2,
45             * x^4, x^8...
46             * -- The result is accumulated, in normal representation, in
47             * the x[] array.
48             * -- t2[] is used as destination buffer for each multiplication.
49             *
50             * Note that there is no need to call br_i32_from_monty().
51             */
52 0           memcpy(t1, x, mlen);
53 0           br_i32_to_monty(t1, m);
54 0           br_i32_zero(x, m[0]);
55 0           x[1] = 1;
56 0 0         for (k = 0; k < ((uint32_t)elen << 3); k ++) {
57             uint32_t ctl;
58              
59 0           ctl = (e[elen - 1 - (k >> 3)] >> (k & 7)) & 1;
60 0           br_i32_montymul(t2, x, t1, m, m0i);
61 0           CCOPY(ctl, x, t2, mlen);
62 0           br_i32_montymul(t2, t1, t1, m, m0i);
63 0           memcpy(t1, t2, mlen);
64             }
65 0           }