Mercurial > dropbear

comparison libtommath/bn_mp_reduce_2k_l.c @ 399:a707e6148060

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
merge of '5fdf69ca60d1683cdd9f4c2595134bed26394834' and '6b61c50f4cf888bea302ac8fcf5dbb573b443251'
author Matt Johnston <matt@ucc.asn.au>
date Sat, 03 Feb 2007 08:20:34 +0000
parents 5ff8218bcee9
children 60fc6476e044
comparison
equal deleted inserted replaced
394:17d097fc111c 399:a707e6148060
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.com
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
59
60 /* $Source: /cvs/libtom/libtommath/bn_mp_reduce_2k_l.c,v $ */
61 /* $Revision: 1.3 $ */
62 /* $Date: 2006/03/31 14:18:44 $ */