1#include <tommath.h>
2#ifdef BN_MP_MUL_2D_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/* shift left by a certain bit count */
19int mp_mul_2d (mp_int * a, int b, mp_int * c)
20{
21  mp_digit d;
22  int      res;
23
24  /* copy */
25  if (a != c) {
26     if ((res = mp_copy (a, c)) != MP_OKAY) {
27       return res;
28     }
29  }
30
31  if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) {
32     if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
33       return res;
34     }
35  }
36
37  /* shift by as many digits in the bit count */
38  if (b >= (int)DIGIT_BIT) {
39    if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
40      return res;
41    }
42  }
43
44  /* shift any bit count < DIGIT_BIT */
45  d = (mp_digit) (b % DIGIT_BIT);
46  if (d != 0) {
47    register mp_digit *tmpc, shift, mask, r, rr;
48    register int x;
49
50    /* bitmask for carries */
51    mask = (((mp_digit)1) << d) - 1;
52
53    /* shift for msbs */
54    shift = DIGIT_BIT - d;
55
56    /* alias */
57    tmpc = c->dp;
58
59    /* carry */
60    r    = 0;
61    for (x = 0; x < c->used; x++) {
62      /* get the higher bits of the current word */
63      rr = (*tmpc >> shift) & mask;
64
65      /* shift the current word and OR in the carry */
66      *tmpc = ((*tmpc << d) | r) & MP_MASK;
67      ++tmpc;
68
69      /* set the carry to the carry bits of the current word */
70      r = rr;
71    }
72
73    /* set final carry */
74    if (r != 0) {
75       c->dp[(c->used)++] = r;
76    }
77  }
78  mp_clamp (c);
79  return MP_OKAY;
80}
81#endif
82
83/* $Source: /cvs/libtom/libtommath/bn_mp_mul_2d.c,v $ */
84/* $Revision: 1.3 $ */
85/* $Date: 2006/03/31 14:18:44 $ */
86