1 /* $NetBSD: bn_mp_lshd.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $ */
2
3 #include <tommath.h>
4 #ifdef BN_MP_LSHD_C
5 /* LibTomMath, multiple-precision integer library -- Tom St Denis
6 *
7 * LibTomMath is a library that provides multiple-precision
8 * integer arithmetic as well as number theoretic functionality.
9 *
10 * The library was designed directly after the MPI library by
11 * Michael Fromberger but has been written from scratch with
12 * additional optimizations in place.
13 *
14 * The library is free for all purposes without any express
15 * guarantee it works.
16 *
17 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
18 */
19
20 /* shift left a certain amount of digits */
mp_lshd(mp_int * a,int b)21 int mp_lshd (mp_int * a, int b)
22 {
23 int x, res;
24
25 /* if its less than zero return */
26 if (b <= 0) {
27 return MP_OKAY;
28 }
29
30 /* grow to fit the new digits */
31 if (a->alloc < a->used + b) {
32 if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
33 return res;
34 }
35 }
36
37 {
38 register mp_digit *top, *bottom;
39
40 /* increment the used by the shift amount then copy upwards */
41 a->used += b;
42
43 /* top */
44 top = a->dp + a->used - 1;
45
46 /* base */
47 bottom = a->dp + a->used - 1 - b;
48
49 /* much like mp_rshd this is implemented using a sliding window
50 * except the window goes the otherway around. Copying from
51 * the bottom to the top. see bn_mp_rshd.c for more info.
52 */
53 for (x = a->used - 1; x >= b; x--) {
54 *top-- = *bottom--;
55 }
56
57 /* zero the lower digits */
58 top = a->dp;
59 for (x = 0; x < b; x++) {
60 *top++ = 0;
61 }
62 }
63 return MP_OKAY;
64 }
65 #endif
66
67 /* Source: /cvs/libtom/libtommath/bn_mp_lshd.c,v */
68 /* Revision: 1.4 */
69 /* Date: 2006/12/28 01:25:13 */
70