[Haskell-cafe] [Haskell-beginners] Int V.S. Word32

[Haisheng Wu]

Hmm... I think I made a little confusion so I put my finding here:
http://haisgwu.info/posts/2011-11-20-euler-problem-14.html

I do got stack overflow thus need several compile opts to fix it.
Not sure if it is what you mean by "You get overflow using 32-bit types
here."

-Haisheng


On Sat, Nov 19, 2011 at 10:49 PM, Daniel Fischer <
daniel.is.fischer at googlemail.com> wrote:

> On Saturday 19 November 2011, 09:09:50, Haisheng Wu wrote:
> > Hello,
> >   I got great performance difference for the following code if I used
> > type `Int` rather than `Data.Word.Word32`.
> >   Anyone can help to explain why such difference?
>
> Short answer: GHC optimises Int calculations far better than Word32
> calculations, rather, it optimises more calculations for Int than for
> Word32.  It also optimises more calculations for Word than for Word32, but
> not as many as for Int.
>
> The reason is that Int (and Word) are (at least expected to be) far more
> often used, so the effort has gone to these types primarily. Work is being
> done to get the fixed-width types on par, but it's not around the corner
> yet.
>
> You can try using Word instead of Word32, that's likely to be faster.
>
> But
>
> >   Thanks a lot.
> >
> > -Simon
> >
> > module Main where
> > import Data.Word
> >
> > main :: IO ()
> > main = print $ p14
> >
> > p14 = maximum [ (startChain n 0, n) | n <- [2..1000000] ]
>
> You get overflow using 32-bit types here.
>
> >
> > startChain :: Word32 -> Int -> Int
> > startChain 1 count    = count + 1
> > startChain n count    = startChain (intTransform n) (count+1)
> >
> > intTransform :: Word32 -> Word32
> > intTransform n
> >
> >   | even n         = n `div` 2
> >   | otherwise      = 3 * n + 1
>
>
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