@Override
  public int hashCode() {
    int hash = 1;
    for (int i = offset; i < offset + length; i++)
      hash = (31 * hash) + (int) bytes[i];
    return hash;
  }
Return the offset into the buffer.
hbase-common/src/main/java/org/apache/hadoop/hbase/io/ImmutableBytesWritable.java