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