crc16.py

TABLE = [
  0, 4129, 8258, 12387, 16516, 20645, 24774, 28903, 33032, 37161, 41290, 
  45419, 49548, 53677, 57806, 61935, 4657, 528, 12915, 8786, 21173, 17044, 
  29431, 25302, 37689, 33560, 45947, 41818, 54205, 50076, 62463, 58334, 9314, 
  13379, 1056, 5121, 25830, 29895, 17572, 21637, 42346, 46411, 34088, 38153, 
  58862, 62927, 50604, 54669, 13907, 9842, 5649, 1584, 30423, 26358, 22165, 
  18100, 46939, 42874, 38681, 34616, 63455, 59390, 55197, 51132, 18628, 22757, 
  26758, 30887, 2112, 6241, 10242, 14371, 51660, 55789, 59790, 63919, 35144, 
  39273, 43274, 47403, 23285, 19156, 31415, 27286, 6769, 2640, 14899, 10770, 
  56317, 52188, 64447, 60318, 39801, 35672, 47931, 43802, 27814, 31879, 19684, 
  23749, 11298, 15363, 3168, 7233, 60846, 64911, 52716, 56781, 44330, 48395, 
  36200, 40265, 32407, 28342, 24277, 20212, 15891, 11826, 7761, 3696, 65439, 
  61374, 57309, 53244, 48923, 44858, 40793, 36728, 37256, 33193, 45514, 41451, 
  53516, 49453, 61774, 57711, 4224, 161, 12482, 8419, 20484, 16421, 28742, 
  24679, 33721, 37784, 41979, 46042, 49981, 54044, 58239, 62302, 689, 4752, 
  8947, 13010, 16949, 21012, 25207, 29270, 46570, 42443, 38312, 34185, 62830, 
  58703, 54572, 50445, 13538, 9411, 5280, 1153, 29798, 25671, 21540, 17413, 
  42971, 47098, 34713, 38840, 59231, 63358, 50973, 55100, 9939, 14066, 1681, 
  5808, 26199, 30326, 17941, 22068, 55628, 51565, 63758, 59695, 39368, 35305, 
  47498, 43435, 22596, 18533, 30726, 26663, 6336, 2273, 14466, 10403, 52093, 
  56156, 60223, 64286, 35833, 39896, 43963, 48026, 19061, 23124, 27191, 31254, 
  2801, 6864, 10931, 14994, 64814, 60687, 56684, 52557, 48554, 44427, 40424, 
  36297, 31782, 27655, 23652, 19525, 15522, 11395, 7392, 3265, 61215, 65342, 
  53085, 57212, 44955, 49082, 36825, 40952, 28183, 32310, 20053, 24180, 11923, 
  16050, 3793, 7920
]


def crc16(buf, start=None, end=None):
  if start is None:
    start = 0
  if end is None:
    end = len(buf)
  num = 0
  for i in range(start, end):
    num = ((num<<8)&0xff00) ^ TABLE[((num>>8)&0xff)^ord(buf[i])]
  return num & 0xffff