1#include <tommath.h>
2#ifdef BN_MP_MUL_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://math.libtomcrypt.com
16 */
17
18/* b = a*2 */
19int mp_mul_2(mp_int * a, mp_int * b)
20{
21  int     x, res, oldused;
22
23  /* grow to accomodate result */
24  if (b->alloc < a->used + 1) {
25    if ((res = mp_grow (b, a->used + 1)) != MP_OKAY) {
26      return res;
27    }
28  }
29
30  oldused = b->used;
31  b->used = a->used;
32
33  {
34    register mp_digit r, rr, *tmpa, *tmpb;
35
36    /* alias for source */
37    tmpa = a->dp;
38
39    /* alias for dest */
40    tmpb = b->dp;
41
42    /* carry */
43    r = 0;
44    for (x = 0; x < a->used; x++) {
45
46      /* get what will be the *next* carry bit from the
47       * MSB of the current digit
48       */
49      rr = *tmpa >> ((mp_digit)(DIGIT_BIT - 1));
50
51      /* now shift up this digit, add in the carry [from the previous] */
52      *tmpb++ = ((*tmpa++ << ((mp_digit)1)) | r) & MP_MASK;
53
54      /* copy the carry that would be from the source
55       * digit into the next iteration
56       */
57      r = rr;
58    }
59
60    /* new leading digit? */
61    if (r != 0) {
62      /* add a MSB which is always 1 at this point */
63      *tmpb = 1;
64      ++(b->used);
65    }
66
67    /* now zero any excess digits on the destination
68     * that we didn't write to
69     */
70    tmpb = b->dp + b->used;
71    for (x = b->used; x < oldused; x++) {
72      *tmpb++ = 0;
73    }
74  }
75  b->sign = a->sign;
76  return MP_OKAY;
77}
78#endif
79
80/* $Source: /cvs/libtom/libtommath/bn_mp_mul_2.c,v $ */
81/* $Revision: 1.3 $ */
82/* $Date: 2006/03/31 14:18:44 $ */
83