tempering32Modified.hs

import           Data.Bits
import           Data.Word
import           Data.STRef
import           Control.Monad.ST

import           Data.Function

import           Test.Hspec
import           Test.Hspec.QuickCheck

main :: IO ()
main = hspec $ do
  prop "tempering32Modified behaves like tempering32" $ \wd ->
    tempering32Modified wd `shouldBe` tempering32 wd
  prop "tempering32Modified2 behaves like tempering32" $ \wd ->
    tempering32Modified2 wd `shouldBe` tempering32 wd


tempering32   :: Word32 -> Word32
tempering32 x =  runST $ do res  <- newSTRef (x :: Word32)
                            res' <- readSTRef res
                            modifySTRef res (xor  (res' `shiftR` 11))
                            res' <- readSTRef res
                            modifySTRef res (xor ((res' `shiftL`  7) .&. (0x9d2c5680 :: Word32)))
                            res' <- readSTRef res
                            modifySTRef res (xor ((res' `shiftL` 15) .&. (0xefc60000 :: Word32)))
                            res' <- readSTRef res
                            modifySTRef res (xor  (res' `shiftR` 18))
                            readSTRef res

tempering32Modified  :: Word32 -> Word32
tempering32Modified x = runST $ do
  res  <- newSTRef (x :: Word32)
  modifySTRef res $ \v -> xor (v `shiftR` 11) v
  modifySTRef res $ \v -> xor ((v `shiftL`  7) .&. (0x9d2c5680 :: Word32)) v
  modifySTRef res $ \v -> xor ((v `shiftL` 15) .&. (0xefc60000 :: Word32)) v
  modifySTRef res $ \v -> xor (v `shiftR` 18) v
  readSTRef res

tempering32Modified2  :: Word32 -> Word32
tempering32Modified2 x =
  x
    & (\v -> xor (v `shiftR` 11) v)
    & (\v -> xor ((v `shiftL`  7) .&. (0x9d2c5680 :: Word32)) v)
    & (\v -> xor ((v `shiftL` 15) .&. (0xefc60000 :: Word32)) v)
    & (\v -> xor (v `shiftR` 18) v)