private static byte[] fastPathRead(InputStream in, int length) throws IOException {
    byte[] result = new byte[length];
    for (int i = 0; i < length; i++) {
      result[i] = (byte) in.read();
    }
    return result;
  }
Unpack the bitpacked HyperLogLog register.
@param in
         - input stream
@param length
         - serialized length
@return unpacked HLL register
@throws IOException
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/common/ndv/hll/HyperLogLogUtils.java