Line data    Source code

       1             : #include "tommath_private.h"
       2             : #ifdef BN_MP_CNT_LSB_C
       3             : /* LibTomMath, multiple-precision integer library -- Tom St Denis */
       4             : /* SPDX-License-Identifier: Unlicense */
       5             : 
       6             : static const int lnz[16] = {
       7             :    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
       8             : };
       9             : 
      10             : /* Counts the number of lsbs which are zero before the first zero bit */
      11           0 : int mp_cnt_lsb(const mp_int *a)
      12             : {
      13             :    int x;
      14             :    mp_digit q, qq;
      15             : 
      16             :    /* easy out */
      17           0 :    if (MP_IS_ZERO(a)) {
      18           0 :       return 0;
      19             :    }
      20             : 
      21             :    /* scan lower digits until non-zero */
      22           0 :    for (x = 0; (x < a->used) && (a->dp[x] == 0u); x++) {}
      23           0 :    q = a->dp[x];
      24           0 :    x *= MP_DIGIT_BIT;
      25             : 
      26             :    /* now scan this digit until a 1 is found */
      27           0 :    if ((q & 1u) == 0u) {
      28             :       do {
      29           0 :          qq  = q & 15u;
      30           0 :          x  += lnz[qq];
      31           0 :          q >>= 4;
      32           0 :       } while (qq == 0u);
      33             :    }
      34           0 :    return x;
      35             : }
      36             : 
      37             : #endif