1 {-# LANGUAGE OverloadedStrings #-}
8 import Control.Monad.State
9 import qualified Data.ByteString.Char8 as BS
10 import qualified Data.ByteString.Lazy as BL
11 import Data.Digest.Adler32 (adler32)
12 import qualified Data.Map as M
13 import Data.Word (Word8, Word32)
14 import qualified Crypto.Hash.MD4 as MD4
16 type Md4digest = BS.ByteString
17 type Adler32checksum = Word32
19 type Signature = (Md4digest, Adler32checksum, Int)
21 fileSignatures :: BL.ByteString -> Integer -> [Signature]
22 fileSignatures bs blockSize = zip3 strongsigs weaksigs [0..]
23 where strongsigs = map blockSig (splitBS bs blockSize)
24 weaksigs = map adler32 (splitBS bs blockSize)
26 splitBS :: BL.ByteString -> Integer -> [BL.ByteString]
27 splitBS bs blockSize | fromIntegral (BL.length bs) < blockSize = [bs]
28 splitBS bs blockSize = BL.take (fromIntegral blockSize) bs :
29 splitBS (BL.drop (fromIntegral blockSize) bs) blockSize
31 -- compute md4 digest (128 bits)
32 blockSig :: BL.ByteString -> BS.ByteString
33 blockSig = MD4.hash . BL.toStrict
35 weakSig :: BL.ByteString -> Adler32checksum
38 data Instruction = RChar Word8
42 genInstructions :: [Signature] -> Integer -> BL.ByteString -> [Instruction]
43 genInstructions f0sigs blockSize fnew =
46 go :: BL.ByteString -> State Word32 [Instruction]
47 go fnew | fnew == BL.empty = return []
49 let (blk, blks) = BL.splitAt (fromIntegral blockSize) fnew
50 adlerSum = weakSig blk
51 matches = M.lookup adlerSum f0AdlerTable >>
52 M.lookup (blockSig blk) f0MD4Table
57 return $ RBlk (head idxs) : is
60 is <- go (BL.tail (blk `mappend` blks))
61 return $ RChar (BL.head blk) : is
62 f0AdlerTable = toAdlerMap f0sigs
63 f0MD4Table = toMD4Map f0sigs
65 toAdlerMap :: [Signature] -> M.Map Adler32checksum [Int]
66 toAdlerMap = foldr f M.empty
67 where f sig m = let (_, aSig, idx) = sig in M.insertWith (++) aSig [idx] m
69 toMD4Map :: [Signature] -> M.Map Md4digest [Int]
70 toMD4Map = foldr f M.empty
71 where f sig m = let (mSig, _, idx) = sig in M.insertWith (++) mSig [idx] m
73 recreate :: BL.ByteString -> Integer -> [Instruction] -> BL.ByteString
74 recreate f0 blockSize ins =
75 let f0blocks = splitBS f0 blockSize
78 where go f0blocks [] = mempty
79 go f0blocks (inst:insts) =
81 RBlk i -> (f0blocks !! i) `mappend` go f0blocks insts
82 RChar w -> BL.singleton w `mappend` go f0blocks insts