code: private void fixFirstEmptyWord()
    {
      int i = firstEmptyWord - 1;
      final int[] localWords = words; // faster
      while (i >= 0 && localWords[i] == 0) {
        i--;
      }
      firstEmptyWord = i + 1;
    }
docs: Sets the field {@link #firstEmptyWord} with the logical size in words of the
  bit set.