gistfile1.hs

{-# LANGUAGE BangPatterns #-}
import           Data.Digest.Adler32 (adler32)
import           Data.ByteString (ByteString)
import qualified Data.ByteString as BS
import           System.IO
import           Data.Word

updateHash :: Word32 -> Word8 -> Word32 -> Word8 -> Word32
updateHash _winlen old8 !hash word8 = hash + (fromIntegral $ old8 + word8)
{- actual adler32 sliding window code goes here -}

updateHash' :: ByteString -> Word32 -> Int -> Word32 -> Word8 -> Word32
updateHash' bs winlen oldpos =
  updateHash winlen old
  where
    old = {-# SCC "BS.index" #-} (BS.index bs oldpos)
    
runWindow :: Word32 -> ByteString -> Word32
runWindow winlen bs =
  let (inits, rest) = BS.splitAt (fromIntegral winlen) bs
  
      updatefn :: (Int, Word32) -> Word8 -> (Int, Word32)
      updatefn = \(oldp, !hash) word ->
                    (oldp + 1, updateHash' bs winlen oldp hash word)

  in snd $ BS.foldl updatefn (0, (adler32 inits)) rest

main = do
  bytes <- withFile "/dev/urandom" ReadMode ((flip BS.hGet) 16777216)
  return $! runWindow 8 bytes