public static long createBlockId(long containerId, long sequenceNumber) {
    // TODO(gene): Check for valid IDs here?
    return ((containerId & CONTAINER_ID_MASK) << SEQUENCE_NUMBER_BITS)
        | (sequenceNumber & SEQUENCE_NUMBER_MASK);
  }
@Test
  public void createBlockId() {
    assertEquals(16797216L, BlockId.createBlockId(1, 20000L));
    assertEquals(20000L, BlockId.createBlockId(0, 20000L));
    assertEquals(2071248101952L, BlockId.createBlockId(123456, 123456L));
  }