1 /* $NetBSD: bn_mp_div_2.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $ */
2
3 #include <tommath.h>
4 #ifdef BN_MP_DIV_2_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 /* b = a/2 */
mp_div_2(mp_int * a,mp_int * b)21 int mp_div_2(mp_int * a, mp_int * b)
22 {
23 int x, res, oldused;
24
25 /* copy */
26 if (b->alloc < a->used) {
27 if ((res = mp_grow (b, a->used)) != MP_OKAY) {
28 return res;
29 }
30 }
31
32 oldused = b->used;
33 b->used = a->used;
34 {
35 register mp_digit r, rr, *tmpa, *tmpb;
36
37 /* source alias */
38 tmpa = a->dp + b->used - 1;
39
40 /* dest alias */
41 tmpb = b->dp + b->used - 1;
42
43 /* carry */
44 r = 0;
45 for (x = b->used - 1; x >= 0; x--) {
46 /* get the carry for the next iteration */
47 rr = *tmpa & 1;
48
49 /* shift the current digit, add in carry and store */
50 *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));
51
52 /* forward carry to next iteration */
53 r = rr;
54 }
55
56 /* zero excess digits */
57 tmpb = b->dp + b->used;
58 for (x = b->used; x < oldused; x++) {
59 *tmpb++ = 0;
60 }
61 }
62 b->sign = a->sign;
63 mp_clamp (b);
64 return MP_OKAY;
65 }
66 #endif
67
68 /* Source: /cvs/libtom/libtommath/bn_mp_div_2.c,v */
69 /* Revision: 1.4 */
70 /* Date: 2006/12/28 01:25:13 */
71