CharMatcher precomputedInternal() {
    final BitSet table = new BitSet();
    setBits(table);
    int totalCharacters = table.cardinality();
    if (totalCharacters * 2 <= DISTINCT_CHARS) {
      return precomputedPositive(totalCharacters, table, toString());
    } else {
      // TODO(lowasser): is it worth it to worry about the last character of large matchers?
      table.flip(Character.MIN_VALUE, Character.MAX_VALUE + 1);