Thanks. > Fusing the ws is trickier. Directly appealing to the fibonacci-number > example is not recommended because this would mean to keep the last 16 > ws in memory and shifting them right to left by hand. But as the
Are you saying this because we don't want a 16-tuple? > "Alternate method of computation" on the website suggests, you can > delegate the shifting to an index that shifts around mod 16. Having a > mutable array is helpful, then. Are you saying that because haskell doesn't really have mutable arrays, this is ruled out? > Of course, you can also fill a large static (boxed!) array of 80 Word8s via > > ws :: Data.Array.IArray.Array Int Word8 > ws = accumArray 0 (0,80) (curry snd) $ > zip [0..15] xs ++ [(i, xxor i) | i<-[16..80]] > where > xxor i = ws ! (i-16) `xor` > ws ! (i-3) `xor` ws ! (i-8) `xor` ws ! (i-14) > > or something like that (I didn't care about correct indices and bounds). > GHC can fuse such array accumulations. Why is an array better than a list? Is it because (!) is O(1) and (!!) is O(n)? > > In general, keeping stuff in lists is not wrong, but ByteStrings are > more adapted to current CPU and RAM architecture. I'm not clear how ByteStrings help here. We need to put bits into 32 words and operate on these. Dominic. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
