1/*	$NetBSD$	*/
2
3#include <tommath.h>
4#ifdef BN_MP_RSHD_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/* shift right a certain amount of digits */
21void mp_rshd (mp_int * a, int b)
22{
23  int     x;
24
25  /* if b <= 0 then ignore it */
26  if (b <= 0) {
27    return;
28  }
29
30  /* if b > used then simply zero it and return */
31  if (a->used <= b) {
32    mp_zero (a);
33    return;
34  }
35
36  {
37    register mp_digit *bottom, *top;
38
39    /* shift the digits down */
40
41    /* bottom */
42    bottom = a->dp;
43
44    /* top [offset into digits] */
45    top = a->dp + b;
46
47    /* this is implemented as a sliding window where
48     * the window is b-digits long and digits from
49     * the top of the window are copied to the bottom
50     *
51     * e.g.
52
53     b-2 | b-1 | b0 | b1 | b2 | ... | bb |   ---->
54                 /\                   |      ---->
55                  \-------------------/      ---->
56     */
57    for (x = 0; x < (a->used - b); x++) {
58      *bottom++ = *top++;
59    }
60
61    /* zero the top digits */
62    for (; x < a->used; x++) {
63      *bottom++ = 0;
64    }
65  }
66
67  /* remove excess digits */
68  a->used -= b;
69}
70#endif
71
72/* Source: /cvs/libtom/libtommath/bn_mp_rshd.c,v */
73/* Revision: 1.4 */
74/* Date: 2006/12/28 01:25:13 */
75