Line data    Source code

       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             : 
      18             : static 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 */
      23           0 : int mp_cnt_lsb(mp_int *a)
      24             : {
      25             :    int x;
      26             :    mp_digit q, qq;
      27             : 
      28             :    /* easy out */
      29           0 :    if (mp_iszero(a) == 1) {
      30           0 :       return 0;
      31             :    }
      32             : 
      33             :    /* scan lower digits until non-zero */
      34           0 :    for (x = 0; x < a->used && a->dp[x] == 0; x++);
      35           0 :    q = a->dp[x];
      36           0 :    x *= DIGIT_BIT;
      37             : 
      38             :    /* now scan this digit until a 1 is found */
      39           0 :    if ((q & 1) == 0) {
      40             :       do {
      41           0 :          qq  = q & 15;
      42           0 :          x  += lnz[qq];
      43           0 :          q >>= 4;
      44           0 :       } while (qq == 0);
      45             :    }
      46           0 :    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 $ */