private byte[] preprocessMask(byte[] mask) {
    if (!UNSAFE_UNALIGNED) {
      // do nothing
      return mask;
    }
    if (isPreprocessedMask(mask)) return mask;
    for (int i = 0; i < mask.length; i++) {
      if (mask[i] == 0) {
        mask[i] = -1; // 0 -> -1
      } else if (mask[i] == 1) {
        mask[i] = 2;// 1 -> 2
      }
    }
    return mask;
  }
We need to preprocess mask array, as since we treat 2's as unfixed positions and -1 (0xff) as
fixed positions
@return mask array
hbase-client/src/main/java/org/apache/hadoop/hbase/filter/FuzzyRowFilter.java