[Haskell-cafe] Are there performant mutable Arrays in Haskell?
dons at galois.com
Thu Mar 19 12:57:22 EDT 2009
> Hey There,
> I am trying to write a hash-algorithm that in fact is working, but as you might have guessed the problem is the performance :) At the moment I am 40 times worse than the same implementation in C.
> My problem is, I need mutable arrays which are the heart of that hash.
> The algorithm is round-based and within each round I need the value of certain positions in that array.
> At the moment I work with an unboxed ST-Array at the crucial part
> --- snip ---
> test list = runSTUArray $ do
> a_arr <- newListArray (0, 1752) list
> let round i = do
> ain <- readArray a_arr (i-n)
> at0 <- readArray a_arr (i-t0)
> at1 <- readArray a_arr (i-t1)
> at2 <- readArray a_arr (i-t2)
> at3 <- readArray a_arr (i-t3)
> at4 <- readArray a_arr (i-t4)
> let li = ls $ (i - n) mod 16
> ri = rs $ (i - n) mod 16
> writeArray a_arr i $ (step4 li)
> . (step3 ri)
> . (step2 at1 at2 at3 at4)
> $ (step1 ain at0 i)
> mapM_ round [n..(n+t-1)]
> return a_arr
> --- snap ---
> I also played around with peekElemOff and pokeElemOff, but this isn't much faster.
> It took ~30sec with my Haskell-Code while the C-implementation need only ~1sec.
> Is there someone who may have some hints for me, what I can do better, or just
> lead me in the right direction? :)
You should be able to directly translate C into approximmately the same
kind of code using STUArrays.
Make sure to compile with -O2 and use unsafeRead/Write where you also do
unchecked read/writes in C.
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