Mercurial > dropbear

comparison libtommath/bn_mp_reduce_2k.c @ 1436:60fc6476e044

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Update to libtommath v1.0
author Matt Johnston <matt@ucc.asn.au>
date Sat, 24 Jun 2017 22:37:14 +0800
parents 5ff8218bcee9
children 8bba51a55704
comparison
equal deleted inserted replaced
1435:f849a5ca2efc 1436:60fc6476e044
1 #include <tommath.h> 1 #include <tommath_private.h>
2 #ifdef BN_MP_REDUCE_2K_C 2 #ifdef BN_MP_REDUCE_2K_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 * 4 *
5 * LibTomMath is a library that provides multiple-precision 5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality. 6 * integer arithmetic as well as number theoretic functionality.
10 * additional optimizations in place. 10 * additional optimizations in place.
11 * 11 *
12 * The library is free for all purposes without any express 12 * The library is free for all purposes without any express
13 * guarantee it works. 13 * guarantee it works.
14 * 14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.com 15 * Tom St Denis, [email protected], http://libtom.org
16 */ 16 */
17 17
18 /* reduces a modulo n where n is of the form 2**p - d */ 18 /* reduces a modulo n where n is of the form 2**p - d */
19 int mp_reduce_2k(mp_int *a, mp_int *n, mp_digit d) 19 int mp_reduce_2k(mp_int *a, mp_int *n, mp_digit d)
20 { 20 {
21 mp_int q; 21 mp_int q;
22 int p, res; 22 int p, res;
23 23
24 if ((res = mp_init(&q)) != MP_OKAY) { 24 if ((res = mp_init(&q)) != MP_OKAY) {
25 return res; 25 return res;
26 } 26 }
27 27
28 p = mp_count_bits(n); 28 p = mp_count_bits(n);
29 top: 29 top:
30 /* q = a/2**p, a = a mod 2**p */ 30 /* q = a/2**p, a = a mod 2**p */
31 if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) { 31 if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
32 goto ERR; 32 goto ERR;
33 } 33 }
34 34
35 if (d != 1) { 35 if (d != 1) {
36 /* q = q * d */ 36 /* q = q * d */
37 if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) { 37 if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) {
38 goto ERR; 38 goto ERR;
39 } 39 }
40 } 40 }
41 41
42 /* a = a + q */ 42 /* a = a + q */
43 if ((res = s_mp_add(a, &q, a)) != MP_OKAY) { 43 if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
44 goto ERR; 44 goto ERR;
45 } 45 }
46 46
47 if (mp_cmp_mag(a, n) != MP_LT) { 47 if (mp_cmp_mag(a, n) != MP_LT) {
48 s_mp_sub(a, n, a); 48 if ((res = s_mp_sub(a, n, a)) != MP_OKAY) {
49 goto ERR;
50 }
49 goto top; 51 goto top;
50 } 52 }
51 53
52 ERR: 54 ERR:
53 mp_clear(&q); 55 mp_clear(&q);
54 return res; 56 return res;
55 } 57 }
56 58
57 #endif 59 #endif
58 60
59 /* $Source: /cvs/libtom/libtommath/bn_mp_reduce_2k.c,v $ */ 61 /* $Source$ */
60 /* $Revision: 1.3 $ */ 62 /* $Revision$ */
61 /* $Date: 2006/03/31 14:18:44 $ */ 63 /* $Date$ */