1#include <tommath.h>
2#ifdef BN_MP_CNT_LSB_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
18static const int lnz[16] = {
19   4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
20};
21
22/* Counts the number of lsbs which are zero before the first zero bit */
23int mp_cnt_lsb(mp_int *a)
24{
25   int x;
26   mp_digit q, qq;
27
28   /* easy out */
29   if (mp_iszero(a) == 1) {
30      return 0;
31   }
32
33   /* scan lower digits until non-zero */
34   for (x = 0; x < a->used && a->dp[x] == 0; x++);
35   q = a->dp[x];
36   x *= DIGIT_BIT;
37
38   /* now scan this digit until a 1 is found */
39   if ((q & 1) == 0) {
40      do {
41         qq  = q & 15;
42         x  += lnz[qq];
43         q >>= 4;
44      } while (qq == 0);
45   }
46   return x;
47}
48
49#endif
50
51/* $Source: /cvs/libtom/libtommath/bn_mp_cnt_lsb.c,v $ */
52/* $Revision: 1.4 $ */
53/* $Date: 2006/12/28 01:25:13 $ */
54