Am Freitag 16 April 2010 17:41:06 schrieb John Lato:
> > From: Mathieu Boespflug <mb...@tweag.net>
> >
> > Dear haskell-cafe,
> >
> > I implemented the Floyd Warshall algorithm for finding the shortest
> > path in a dense graph in Haskell, but noted the performance was
> > extremely poor compared to C. Even using mutable unboxed arrays it was
> > running about 30 times slower. I rewrote the program several times, to
> > arrive at the following definition:
>
> My results are basically the same as Max's, but if I change
>
> > #define SIZE 1500
>
> to
>
> > sIZE = 1500
>
> and all references from "SIZE" to "sIZE", something ... changes. A lot.
>
> MacBook-1:Desktop johnlato$ time ./FW
> Allocating ...
> Allocating ... done
>
> real 0m0.027s
> user 0m0.013s
> sys 0m0.014s
>
> I can't figure this out at all. Can anyone else confirm, or offer a
> good explanation?
>
let loop1 SIZE = return ()
loop1 k = let loop2 SIZE = return ()
loop2 i = let loop3 SIZE = return ()
loop3 j = do
If you replace SIZE, which will be replaced with the literal 1500 by the
preprocessor, with sIZE, your loops will become trivial:
let loop1 sIZE = return ()
{- deead code -}
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