@Override
  public void init(ByteArrayRef bytes, int start, int length) {
    assert (8 == length);
    data.set(Double.longBitsToDouble(LazyBinaryUtils.byteArrayToLong(bytes
        .getData(), start)));
  }
LazyBinaryObject for double which takes eight bytes.
serde/src/java/org/apache/hadoop/hive/serde2/lazybinary/LazyBinaryDouble.java