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, tomstdenis@gmail.com, http://libtom.org
16 */
17
18/* b = a/2 */
19int 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
65
66/* $Source: /cvs/libtom/libtommath/bn_mp_div_2.c,v $ */
67/* $Revision: 1.4 $ */
68/* $Date: 2006/12/28 01:25:13 $ */
69