1/*	$NetBSD$	*/
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 */
21int 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