Paste: LC53.hs

import Data.Bits
import Control.Monad
import IO
import Char


rndunity = 4294967291 -- 2^32 - 5
rndmult  = 3961633963 -- 2^32 - 333333333

char2integer:: Char -> Integer 
char2integer = toInteger . ord
integer2char:: Integer -> Char
integer2char = chr . fromInteger

prng:: Integer -> Integer
prng    seed  = mod (seed * rndmult) rndunity
rndbyte seed  = (newseed,255 .&. r) 
                where newseed = prng seed
                      r = shiftR newseed 24

crypt:: Integer -> [Integer] -> [Integer]
crypt _    [] = []
crypt seed (x:xs) = (xor x r):(crypt newseed xs)
                    where (newseed,r) = rndbyte seed


testfile = "test.txt"
testseed = 123456789

highbit x = testBit x 7

howfaracc:: Integer-> [Integer] -> Integer -> Integer
howfaracc   _    []    _  = -1
howfaracc seed (x:xs) acc = if found
                               then acc
                               else howfaracc newseed xs (acc+1)
                            where 
                               (newseed,r) = rndbyte seed
                               found = highbit $ xor x r
howfar:: Integer-> [Integer] -> Integer
howfar seed seq = howfaracc seed seq 0

findseed :: [Integer] -> Integer -> Integer -> Integer -> Maybe Integer
findseed _      _          _    0   = Nothing
findseed sample uppercount seed mask = 
                                       let 
                                          tryout = seed .|. mask
                                          count  = howfar tryout sample
                                          finished = (count == -1)
                                       in
                                          if finished
                                          then Just tryout
                                          else 
                                                if uppercount < count
                                                  then mplus
                                                       (findseed sample count       ((.|.) seed mask) nextmask)
                                                       (findseed sample uppercount  seed              nextmask)
                                                  else mplus
                                                       (findseed sample uppercount  seed              nextmask)
                                                       (findseed sample count       ((.|.) seed mask) nextmask)
                                                where 
                                                   nextmask = shiftR mask 1
                                                   
main = do 
      handle <- openFile testfile ReadMode
      sample <- hGetContents handle
      putStrLn "Yosh !"
      putStrLn sample
      let sample1 = crypt testseed $ map (toInteger . ord) sample
      let seed = findseed sample1 0 0 2147483648
      case seed of
        Just a ->  
                do
                  putStrLn $ show a
                  putStrLn $ map ( chr . fromInteger ) sample2
                  where sample2 = crypt a sample1
        Nothing -> do 
                   putStrLn "Failed"