Am Freitag 16 April 2010 17:41:06 schrieb John Lato:
From: Mathieu Boespflug
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 -}