Mercurial > dropbear

comparison libtommath/bn_mp_reduce_2k_l.c @ 293:9d110777f345 contrib-blacklist

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
propagate from branch 'au.asn.ucc.matt.dropbear' (head 7ad1775ed65e75dbece27fe6b65bf1a234db386a) to branch 'au.asn.ucc.matt.dropbear.contrib.blacklist' (head 1d86a4f0a401cc68c2670d821a2f6366c37af143)
author Matt Johnston <matt@ucc.asn.au>
date Fri, 10 Mar 2006 06:31:29 +0000
parents eed26cff980b
children 5ff8218bcee9
comparison
equal deleted inserted replaced
247:c07de41b53d7 293:9d110777f345
1 #include <tommath.h>
2 #ifdef BN_MP_REDUCE_2K_L_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 *
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * The library is free for all purposes without any express
13 * guarantee it works.
14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
16 */
17
18 /* reduces a modulo n where n is of the form 2**p - d
19 This differs from reduce_2k since "d" can be larger
20 than a single digit.
21 */
22 int mp_reduce_2k_l(mp_int *a, mp_int *n, mp_int *d)
23 {
24 mp_int q;
25 int p, res;
26
27 if ((res = mp_init(&q)) != MP_OKAY) {
28 return res;
29 }
30
31 p = mp_count_bits(n);
32 top:
33 /* q = a/2**p, a = a mod 2**p */
34 if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
35 goto ERR;
36 }
37
38 /* q = q * d */
39 if ((res = mp_mul(&q, d, &q)) != MP_OKAY) {
40 goto ERR;
41 }
42
43 /* a = a + q */
44 if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
45 goto ERR;
46 }
47
48 if (mp_cmp_mag(a, n) != MP_LT) {
49 s_mp_sub(a, n, a);
50 goto top;
51 }
52
53 ERR:
54 mp_clear(&q);
55 return res;
56 }
57
58 #endif