Mercurial > dropbear

comparison bn_mp_mul_2d.c @ 1:22d5cf7d4b1a libtommath

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Renaming branch
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:23:46 +0000
parents
children d29b64170cf0
comparison
equal deleted inserted replaced
-1:000000000000 1:22d5cf7d4b1a
1 /* LibTomMath, multiple-precision integer library -- Tom St Denis
2 *
3 * LibTomMath is a library that provides multiple-precision
4 * integer arithmetic as well as number theoretic functionality.
5 *
6 * The library was designed directly after the MPI library by
7 * Michael Fromberger but has been written from scratch with
8 * additional optimizations in place.
9 *
10 * The library is free for all purposes without any express
11 * guarantee it works.
12 *
13 * Tom St Denis, [email protected], http://math.libtomcrypt.org
14 */
15 #include <tommath.h>
16
17 /* shift left by a certain bit count */
18 int mp_mul_2d (mp_int * a, int b, mp_int * c)
19 {
20 mp_digit d;
21 int res;
22
23 /* copy */
24 if (a != c) {
25 if ((res = mp_copy (a, c)) != MP_OKAY) {
26 return res;
27 }
28 }
29
30 if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) {
31 if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
32 return res;
33 }
34 }
35
36 /* shift by as many digits in the bit count */
37 if (b >= (int)DIGIT_BIT) {
38 if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
39 return res;
40 }
41 }
42
43 /* shift any bit count < DIGIT_BIT */
44 d = (mp_digit) (b % DIGIT_BIT);
45 if (d != 0) {
46 register mp_digit *tmpc, shift, mask, r, rr;
47 register int x;
48
49 /* bitmask for carries */
50 mask = (((mp_digit)1) << d) - 1;
51
52 /* shift for msbs */
53 shift = DIGIT_BIT - d;
54
55 /* alias */
56 tmpc = c->dp;
57
58 /* carry */
59 r = 0;
60 for (x = 0; x < c->used; x++) {
61 /* get the higher bits of the current word */
62 rr = (*tmpc >> shift) & mask;
63
64 /* shift the current word and OR in the carry */
65 *tmpc = ((*tmpc << d) | r) & MP_MASK;
66 ++tmpc;
67
68 /* set the carry to the carry bits of the current word */
69 r = rr;
70 }
71
72 /* set final carry */
73 if (r != 0) {
74 c->dp[(c->used)++] = r;
75 }
76 }
77 mp_clamp (c);
78 return MP_OKAY;
79 }