From: Ramakrishnan Muthukrishnan <ram@rkrishnan.org> Date: Mon, 5 Dec 2016 16:20:08 +0000 (+0530) Subject: checksumUpdate refactored/reimplemented X-Git-Url: https://git.rkrishnan.org/%5B/%5D%20/file/URI:LIT:krugkidfnzsc4/@@named=/module-simplejson.scanner.html?a=commitdiff_plain;h=920037d2f6f420237089c00b09be6a6fdf1e9d3c;p=hs-rsync.git checksumUpdate refactored/reimplemented --- diff --git a/src/Lib.hs b/src/Lib.hs index 2ef9cfd..596d94d 100644 --- a/src/Lib.hs +++ b/src/Lib.hs @@ -17,6 +17,8 @@ import qualified Crypto.Hash.MD4 as MD4 type Md4digest = BS.ByteString type Adler32checksum = Word32 +type Checksum = (Word32, Int, Int) + type Signature = (Md4digest, Adler32checksum, Int) fileSignatures :: BL.ByteString -> Integer -> [Signature] @@ -97,15 +99,30 @@ rollingChecksum strtIdx endIdx bs = a `mod` m + ((fromIntegral b) `mod` m) `shif mb = 16 wbs' = BL.zipWith (*) (BL.pack (reverse (map fromIntegral [1..(endIdx - strtIdx + 1)]))) bs' -checksum :: Int -> Int -> BL.ByteString -> Word32 -checksum strtIdx endIdx bs = a `mod` m + ((fromIntegral b) `mod` m) `shiftL` mb - where buffer = map fromIntegral $ take (endIdx - strtIdx) $ drop strtIdx $ BL.unpack bs +checksum :: BL.ByteString -> Int -> Int -> Checksum +checksum bs strtIdx endIdx = (csval, strtIdx, endIdx) + where csval = a `mod` m + ((fromIntegral b) `mod` m) `shiftL` size + buffer = map fromIntegral $ take (endIdx - strtIdx) $ drop strtIdx $ BL.unpack bs indices = map fromIntegral [1..(endIdx - strtIdx + 1)] a = sum buffer b = sum $ zipWith (*) (reverse indices) buffer m = 2^size size = 16 +-- given the checksum a(k, l) and b(k, l), find checksum a(k+1, l+1), b(k+1, l+1) +checksumUpdate :: Checksum -> BL.ByteString -> Checksum +checksumUpdate curCheckSum bs = (csval, oldStrtIdx + 1, oldEndIdx + 1) + where (oldChecksum, oldStrtIdx, oldEndIdx) = curCheckSum + csval = a `mod` m + ((fromIntegral b) `mod` m) `shiftL` size + m = 2^size + size = 16 + bold = oldChecksum `shiftR` size + aold = oldChecksum .&. (m - 1) + xk = head $ drop oldStrtIdx $ BL.unpack bs + xlPlus1 = head $ drop (oldEndIdx + 1) $BL.unpack bs + a = aold - fromIntegral xk + fromIntegral xlPlus1 + b = a + bold - (fromIntegral (oldEndIdx - oldStrtIdx + 1)) + -- given the checksum of bytes from index: startIdx to endIdx, find -- the checksum for the block from (startIdx + 1 .. endIdx + 1) rollingChecksumUpdate :: Word32 -> Word8 -> Word8 -> Integer -> Integer -> Word32