def crc16(data: bytes):
    """ Calculates a CRC-16 CCITT checksum. data should be of type bytes() """
    crc16_table = [0, 4489, 8978, 12955, 17956, 22445, 25910, 29887, 35912,
        40385, 44890, 48851, 51820, 56293, 59774, 63735, 4225, 264, 13203, 
        8730, 22181, 18220, 30135, 25662, 40137, 36160, 49115, 44626, 56045,
        52068, 63999, 59510, 8450, 12427, 528, 5017, 26406, 30383, 17460, 
        21949, 44362, 48323, 36440, 40913, 60270, 64231, 51324, 55797, 
        12675, 8202, 4753, 792, 30631, 26158, 21685, 17724, 48587, 44098, 
        40665, 36688, 64495, 60006, 55549, 51572, 16900, 21389, 24854, 
        28831, 1056, 5545, 10034, 14011, 52812, 57285, 60766, 64727, 34920,
        39393, 43898, 47859, 21125, 17164, 29079, 24606, 5281, 1320, 14259,
        9786, 57037, 53060, 64991, 60502, 39145, 35168, 48123, 43634, 25350,
        29327, 16404, 20893, 9506, 13483, 1584, 6073, 61262, 65223, 52316, 
        56789, 43370, 47331, 35448, 39921, 29575, 25102, 20629, 16668, 
        13731, 9258, 5809, 1848, 65487, 60998, 56541, 52564, 47595, 43106, 
        39673, 35696, 33800, 38273, 42778, 46739, 49708, 54181, 57662, 
        61623, 2112, 6601, 11090, 15067, 20068, 24557, 28022, 31999, 38025,
        34048, 47003, 42514, 53933, 49956, 61887, 57398, 6337, 2376, 15315,
        10842, 24293, 20332, 32247, 27774, 42250, 46211, 34328, 38801, 
        58158, 62119, 49212, 53685, 10562, 14539, 2640, 7129, 28518, 32495,
        19572, 24061, 46475, 41986, 38553, 34576, 62383, 57894, 53437, 
        49460, 14787, 10314, 6865, 2904, 32743, 28270, 23797, 19836, 50700,
        55173, 58654, 62615, 32808, 37281, 41786, 45747, 19012, 23501, 
        26966, 30943, 3168, 7657, 12146, 16123, 54925, 50948, 62879, 58390,
        37033, 33056, 46011, 41522, 23237, 19276, 31191, 26718, 7393, 3432,
        16371, 11898, 59150, 63111, 50204, 54677, 41258, 45219, 33336, 
        37809, 27462, 31439, 18516, 23005, 11618, 15595, 3696, 8185, 63375,
        58886, 54429, 50452, 45483, 40994, 37561, 33584, 31687, 27214, 
        22741, 18780, 15843, 11370, 7921, 3960]
    crc_buff = 65535
    for i in range(len(data)):
        c = data[i]
        crc_buff = crc_buff >> 8 ^ crc16_table[c ^ crc_buff & 255]
    return crc_buff
