|
282
|
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 * |
|
386
|
15 * Tom St Denis, [email protected], http://math.libtomcrypt.com |
|
282
|
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 |
|
386
|
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 $ */ |
