Mercurial > dropbear

comparison bn_mp_lshd.c @ 2:86e0b50a9b58 libtommath-orig ltm-0.30-orig

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
ltm 0.30 orig import
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:25:22 +0000
parents
children d29b64170cf0
comparison
equal deleted inserted replaced
-1:000000000000 2:86e0b50a9b58
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 a certain amount of digits */
18 int mp_lshd (mp_int * a, int b)
19 {
20 int x, res;
21
22 /* if its less than zero return */
23 if (b <= 0) {
24 return MP_OKAY;
25 }
26
27 /* grow to fit the new digits */
28 if (a->alloc < a->used + b) {
29 if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
30 return res;
31 }
32 }
33
34 {
35 register mp_digit *top, *bottom;
36
37 /* increment the used by the shift amount then copy upwards */
38 a->used += b;
39
40 /* top */
41 top = a->dp + a->used - 1;
42
43 /* base */
44 bottom = a->dp + a->used - 1 - b;
45
46 /* much like mp_rshd this is implemented using a sliding window
47 * except the window goes the otherway around. Copying from
48 * the bottom to the top. see bn_mp_rshd.c for more info.
49 */
50 for (x = a->used - 1; x >= b; x--) {
51 *top-- = *bottom--;
52 }
53
54 /* zero the lower digits */
55 top = a->dp;
56 for (x = 0; x < b; x++) {
57 *top++ = 0;
58 }
59 }
60 return MP_OKAY;
61 }