void fp_mod_2d(fp_int *a, int b, fp_int *c)
{
   int x;

   /* zero if count less than or equal to zero */
   if (b <= 0) {
      fp_zero(c);
      return;
   }

   /* get copy of input */
   fp_copy(a, c);

   /* if 2**d is larger than we just return */
   if (b >= (DIGIT_BIT * a->used)) {
      return;
   }

  /* zero digits above the last digit of the modulus */
  for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
    c->dp[x] = 0;
  }
  /* clear the digit that is not completely outside/inside the modulus */
  c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> (DIGIT_BIT - b);
  fp_clamp (c);
}
void fp_mod_2d(fp_int *a, int b, fp_int *c)
{
   int x;

    
   if (b <= 0) {
      fp_zero(c);
      return;
   }

    
   fp_copy(a, c);

    
   if (b >= (DIGIT_BIT * a->used)) {
      return;
   }

   
  for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
    c->dp[x] = 0;
  }
   
  c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> (DIGIT_BIT - b);
  fp_clamp (c);
}