def _tif_initial(by: bytes) ->int:
    """Basic LIS with TIF markers correctly written.
    Checks 8 bytes exactly so 2^64.
    """
    assert len(by
        ) >= 8, f'_lis_tif_initial(): needs at least 8 bytes not {len(by):d}'
    if by[:4] != b'\x00\x00\x00\x00':
        return 1
    if by[4:8] != b'\x00\x00\x00\x00':
        return 2
    return 0
