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comparison bn_mp_div_2.c @ 2:86e0b50a9b58 libtommath-orig ltm-0.30-orig

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ltm 0.30 orig import
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:25:22 +0000
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children d29b64170cf0
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-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 /* b = a/2 */
18 int mp_div_2(mp_int * a, mp_int * b)
19 {
20 int x, res, oldused;
21
22 /* copy */
23 if (b->alloc < a->used) {
24 if ((res = mp_grow (b, a->used)) != MP_OKAY) {
25 return res;
26 }
27 }
28
29 oldused = b->used;
30 b->used = a->used;
31 {
32 register mp_digit r, rr, *tmpa, *tmpb;
33
34 /* source alias */
35 tmpa = a->dp + b->used - 1;
36
37 /* dest alias */
38 tmpb = b->dp + b->used - 1;
39
40 /* carry */
41 r = 0;
42 for (x = b->used - 1; x >= 0; x--) {
43 /* get the carry for the next iteration */
44 rr = *tmpa & 1;
45
46 /* shift the current digit, add in carry and store */
47 *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));
48
49 /* forward carry to next iteration */
50 r = rr;
51 }
52
53 /* zero excess digits */
54 tmpb = b->dp + b->used;
55 for (x = b->used; x < oldused; x++) {
56 *tmpb++ = 0;
57 }
58 }
59 b->sign = a->sign;
60 mp_clamp (b);
61 return MP_OKAY;
62 }