c3-lang/libtommath/bn_mp_cnt_lsb.c

• Show log

  Commit

• Hash : e45f75fd
  Author :
  Date : 2019-04-13T08:46:57
  

  deprecate DIGIT_BIT, use MP_DIGIT_BIT

Download

• bn_mp_cnt_lsb.c

• #include "tommath_private.h"
  #ifdef BN_MP_CNT_LSB_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  static const int lnz[16] = {
     4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
  };
  
  /* Counts the number of lsbs which are zero before the first zero bit */
  int mp_cnt_lsb(const mp_int *a)
  {
     int x;
     mp_digit q, qq;
  
     /* easy out */
     if (MP_IS_ZERO(a)) {
        return 0;
     }
  
     /* scan lower digits until non-zero */
     for (x = 0; (x < a->used) && (a->dp[x] == 0u); x++) {}
     q = a->dp[x];
     x *= MP_DIGIT_BIT;
  
     /* now scan this digit until a 1 is found */
     if ((q & 1u) == 0u) {
        do {
           qq  = q & 15u;
           x  += lnz[qq];
           q >>= 4;
        } while (qq == 0u);
     }
     return x;
  }
  
  #endif
  

Download