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comparison libtommath/bn_mp_div_2.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_DIV_2_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 /* b = a/2 */
19 int mp_div_2(mp_int * a, mp_int * b)
20 {
21 int x, res, oldused;
22
23 /* copy */
24 if (b->alloc < a->used) {
25 if ((res = mp_grow (b, a->used)) != MP_OKAY) {
26 return res;
27 }
28 }
29
30 oldused = b->used;
31 b->used = a->used;
32 {
33 register mp_digit r, rr, *tmpa, *tmpb;
34
35 /* source alias */
36 tmpa = a->dp + b->used - 1;
37
38 /* dest alias */
39 tmpb = b->dp + b->used - 1;
40
41 /* carry */
42 r = 0;
43 for (x = b->used - 1; x >= 0; x--) {
44 /* get the carry for the next iteration */
45 rr = *tmpa & 1;
46
47 /* shift the current digit, add in carry and store */
48 *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));
49
50 /* forward carry to next iteration */
51 r = rr;
52 }
53
54 /* zero excess digits */
55 tmpb = b->dp + b->used;
56 for (x = b->used; x < oldused; x++) {
57 *tmpb++ = 0;
58 }
59 }
60 b->sign = a->sign;
61 mp_clamp (b);
62 return MP_OKAY;
63 }
64 #endif