From: Ramakrishnan Muthukrishnan Date: Sun, 4 Dec 2016 15:11:49 +0000 (+0530) Subject: rewrite checksum calculation X-Git-Url: https://git.rkrishnan.org/%5B/%5D%20/file/URI:LIT:krugkidfnzsc4/frontends/cyclelanguage?a=commitdiff_plain;h=05f93afdf76cddbf61cd46cb196e5c340d1a09b9;p=hs-rsync.git rewrite checksum calculation --- diff --git a/src/Lib.hs b/src/Lib.hs index fc597cc..2ef9cfd 100644 --- a/src/Lib.hs +++ b/src/Lib.hs @@ -6,10 +6,10 @@ module Lib ) where import Control.Monad.State -import Data.Bits (shiftR, (.&.)) +import Data.Bits (shiftL, shiftR, (.&.)) import qualified Data.ByteString.Char8 as BS import qualified Data.ByteString.Lazy as BL -import Data.Digest.Adler32 (adler32, adler32Update) +import Data.Digest.Adler32 (adler32) import qualified Data.Map as M import Data.Word (Word8, Word32) import qualified Crypto.Hash.MD4 as MD4 @@ -55,12 +55,15 @@ genInstructions f0sigs blockSize fnew = M.lookup (blockSig blk) f0MD4Table case matches of Just idxs -> do - modify (`adler32Update` blk) + -- modify (`adler32Update` blk) + put $ rollingChecksum (fromIntegral startIdx) (fromIntegral endIdx) fnew is <- go (endIdx + 1) blks return $ RBlk (head idxs) : is Nothing -> do - let c = BL.head blk - modify (`adler32Update` BL.singleton c) + let c = BL.head blk + c' = BL.head blk -- FIX (should have been blks) + -- modify (`adler32Update` BL.singleton c) + put $ rollingChecksumUpdate adlerSum c c' startIdx endIdx is <- go (startIdx + 1) (BL.tail (blk `mappend` blks)) return $ RChar c : is f0AdlerTable = toAdlerMap f0sigs @@ -86,12 +89,22 @@ recreate f0 blockSize ins = RChar w -> BL.singleton w `mappend` go f0blocks insts rollingChecksum :: Int -> Int -> BL.ByteString -> Word32 -rollingChecksum strtIdx lenBS bs = a `mod` m + ((fromIntegral b) `mod` m) * m +rollingChecksum strtIdx endIdx bs = a `mod` m + ((fromIntegral b) `mod` m) `shiftL` mb where a = BL.foldl (\acc x -> acc + (fromIntegral x)) 0 bs' b = BL.foldl (\acc x -> acc + x) 0 (BL.pack wbs') - bs' = BL.take (fromIntegral lenBS) $ BL.drop (fromIntegral strtIdx) bs + bs' = BL.take (fromIntegral (endIdx - strtIdx + 1)) bs m = 2^16 - wbs' = BL.zipWith (*) (BL.pack (reverse (map fromIntegral [1..(lenBS - strtIdx + 1)]))) bs' + 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 + indices = map fromIntegral [1..(endIdx - strtIdx + 1)] + a = sum buffer + b = sum $ zipWith (*) (reverse indices) buffer + m = 2^size + size = 16 -- given the checksum of bytes from index: startIdx to endIdx, find -- the checksum for the block from (startIdx + 1 .. endIdx + 1)