private boolean isPreprocessedMask(byte[] mask) {
    for (int i = 0; i < mask.length; i++) {
      if (mask[i] != -1 && mask[i] != 2) {
        return false;
      }
    }
    return true;
  }
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