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comparison libtommath/bn_mp_lshd.c @ 284:eed26cff980b

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propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
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children 5ff8218bcee9
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283:bd240aa12ba7 284:eed26cff980b
1 #include <tommath.h>
2 #ifdef BN_MP_LSHD_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 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
16 */
17
18 /* shift left a certain amount of digits */
19 int mp_lshd (mp_int * a, int b)
20 {
21 int x, res;
22
23 /* if its less than zero return */
24 if (b <= 0) {
25 return MP_OKAY;
26 }
27
28 /* grow to fit the new digits */
29 if (a->alloc < a->used + b) {
30 if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
31 return res;
32 }
33 }
34
35 {
36 register mp_digit *top, *bottom;
37
38 /* increment the used by the shift amount then copy upwards */
39 a->used += b;
40
41 /* top */
42 top = a->dp + a->used - 1;
43
44 /* base */
45 bottom = a->dp + a->used - 1 - b;
46
47 /* much like mp_rshd this is implemented using a sliding window
48 * except the window goes the otherway around. Copying from
49 * the bottom to the top. see bn_mp_rshd.c for more info.
50 */
51 for (x = a->used - 1; x >= b; x--) {
52 *top-- = *bottom--;
53 }
54
55 /* zero the lower digits */
56 top = a->dp;
57 for (x = 0; x < b; x++) {
58 *top++ = 0;
59 }
60 }
61 return MP_OKAY;
62 }
63 #endif