{-# LANGUAGE TypeFamilies #-}
module Data.Digest.CRC8
    ( CRC8(..)
    ) where


-------------------------------------------------------------------------------
import           Data.Bits
import           Data.ByteString     as BS
import           Data.Vector.Unboxed as V
import           Data.Word
-------------------------------------------------------------------------------
import           Data.Digest.CRC
-------------------------------------------------------------------------------


newtype CRC8 = CRC8 { crc8 :: Word8 } deriving (Show, Eq, Ord)


instance CRC CRC8 where
  type CRCWord CRC8 = Word8
  initCRC = CRC8 0
  crcWord = crc8
  updateDigest = updateDigest8
  crcTable = table


-------------------------------------------------------------------------------
updateDigest8 :: CRC8 -> ByteString -> CRC8
updateDigest8 crc = BS.foldl go crc
  where
    go (CRC8 crc') b8 =
      let idx = fromIntegral (crc' `xor` b8) .&. 0xff
      in CRC8 ((table ! idx) `xor` ((crc' `shiftR` 8) .&. 0xff))


-------------------------------------------------------------------------------
table :: V.Vector Word8
table = V.fromList
  [ 0x00, 0x07, 0x0e, 0x09
  , 0x1c, 0x1b, 0x12, 0x15
  , 0x38, 0x3f, 0x36, 0x31
  , 0x24, 0x23, 0x2a, 0x2d
  , 0x70, 0x77, 0x7e, 0x79
  , 0x6c, 0x6b, 0x62, 0x65
  , 0x48, 0x4f, 0x46, 0x41
  , 0x54, 0x53, 0x5a, 0x5d
  , 0xe0, 0xe7, 0xee, 0xe9
  , 0xfc, 0xfb, 0xf2, 0xf5
  , 0xd8, 0xdf, 0xd6, 0xd1
  , 0xc4, 0xc3, 0xca, 0xcd
  , 0x90, 0x97, 0x9e, 0x99
  , 0x8c, 0x8b, 0x82, 0x85
  , 0xa8, 0xaf, 0xa6, 0xa1
  , 0xb4, 0xb3, 0xba, 0xbd
  , 0xc7, 0xc0, 0xc9, 0xce
  , 0xdb, 0xdc, 0xd5, 0xd2
  , 0xff, 0xf8, 0xf1, 0xf6
  , 0xe3, 0xe4, 0xed, 0xea
  , 0xb7, 0xb0, 0xb9, 0xbe
  , 0xab, 0xac, 0xa5, 0xa2
  , 0x8f, 0x88, 0x81, 0x86
  , 0x93, 0x94, 0x9d, 0x9a
  , 0x27, 0x20, 0x29, 0x2e
  , 0x3b, 0x3c, 0x35, 0x32
  , 0x1f, 0x18, 0x11, 0x16
  , 0x03, 0x04, 0x0d, 0x0a
  , 0x57, 0x50, 0x59, 0x5e
  , 0x4b, 0x4c, 0x45, 0x42
  , 0x6f, 0x68, 0x61, 0x66
  , 0x73, 0x74, 0x7d, 0x7a
  , 0x89, 0x8e, 0x87, 0x80
  , 0x95, 0x92, 0x9b, 0x9c
  , 0xb1, 0xb6, 0xbf, 0xb8
  , 0xad, 0xaa, 0xa3, 0xa4
  , 0xf9, 0xfe, 0xf7, 0xf0
  , 0xe5, 0xe2, 0xeb, 0xec
  , 0xc1, 0xc6, 0xcf, 0xc8
  , 0xdd, 0xda, 0xd3, 0xd4
  , 0x69, 0x6e, 0x67, 0x60
  , 0x75, 0x72, 0x7b, 0x7c
  , 0x51, 0x56, 0x5f, 0x58
  , 0x4d, 0x4a, 0x43, 0x44
  , 0x19, 0x1e, 0x17, 0x10
  , 0x05, 0x02, 0x0b, 0x0c
  , 0x21, 0x26, 0x2f, 0x28
  , 0x3d, 0x3a, 0x33, 0x34
  , 0x4e, 0x49, 0x40, 0x47
  , 0x52, 0x55, 0x5c, 0x5b
  , 0x76, 0x71, 0x78, 0x7f
  , 0x6a, 0x6d, 0x64, 0x63
  , 0x3e, 0x39, 0x30, 0x37
  , 0x22, 0x25, 0x2c, 0x2b
  , 0x06, 0x01, 0x08, 0x0f
  , 0x1a, 0x1d, 0x14, 0x13
  , 0xae, 0xa9, 0xa0, 0xa7
  , 0xb2, 0xb5, 0xbc, 0xbb
  , 0x96, 0x91, 0x98, 0x9f
  , 0x8a, 0x8d, 0x84, 0x83
  , 0xde, 0xd9, 0xd0, 0xd7
  , 0xc2, 0xc5, 0xcc, 0xcb
  , 0xe6, 0xe1, 0xe8, 0xef
  , 0xfa, 0xfd, 0xf4, 0xf3
  ]