private boolean compareHashBits(long ref, int hashCode) {
    long fakeRef = Ref.makeFirstRef(0, (byte)0, hashCode, startingHashBitCount);
    return (Ref.getHashBits(fakeRef) == Ref.getHashBits(ref));
  }
Same as {@link #isSameKey(long, int, long, int)} but for externally stored key.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/BytesBytesMultiHashMap.java