Review

class OpenBitSetIterator {
  public int advance(int target) {
    indexArray = 0;
    i = target >> 6;
    if (i >= words) {
      word = 0; // setup so next() will also return -1
      return curDocId = NO_MORE_DOCS;
    }
    wordShift = target & 0x3f;
    word = arr[i] >>> wordShift;
    if (word != 0) {
      wordShift--; // compensate for 1 based arrIndex
    } else {
      while (word == 0) {
        if (++i >= words) {
          return curDocId = NO_MORE_DOCS;
        }
        word = arr[i];
      }
      wordShift = -1;
    }

    shift();

    int bitIndex = (indexArray & 0x0f) + wordShift;
    indexArray >>>= 4;
    // should i<<6 be cached as a separate variable?
    // it would only save one cycle in the best circumstances.
    return curDocId = (i<<6) + bitIndex;
  }

}