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-- CRC24.hs: OpenPGP (RFC4880) CRC24 implementation
-- Copyright © 2012-2019 Clint Adams
-- This software is released under the terms of the ISC license.
-- (See the LICENSE file).
module Data.Digest.CRC24 (
crc24
, crc24Lazy
) where
import Data.Bits (shiftL, (.&.), xor)
import Data.ByteString.Lazy (ByteString)
import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as BL
import Data.Word (Word8, Word32)
crc24Init :: Word32
crc24Init = 0xB704CE
crc24Poly :: Word32
crc24Poly = 0x1864CFB
crc24Update :: Word32 -> Word8 -> Word32
crc24Update c b = (last . take 9 $ iterate (\x -> if shiftL x 1 .&. 0x1000000 == 0x1000000 then shiftL x 1 `xor` crc24Poly else shiftL x 1) (c `xor` shiftL (fromIntegral b) 16)) .&. 0xFFFFFF
crc24 :: B.ByteString -> Word32
crc24 bs = crc24Lazy . BL.fromChunks $ [bs]
crc24Lazy :: ByteString -> Word32
crc24Lazy = BL.foldl' crc24Update crc24Init
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