code: public int last() {
          int val;
          int i;
  
          for (i = data.length - 1; i >= 0; i--) {
              if (data[i] != 0) {
                  val = data[i] >>> 1;
                  i <<= SHIFT;
                  while (val != 0) {
                      val >>>= 1;
                      i++;
                  }
                  return i;
              }
          }
          return -1;
      }
docs: Gets the last element of the set.
  @return   last element of the set, -1 if the set is empty