loop performance bug

[Lemmih]

On Tue, 15 Mar 2005 02:06:06 +0100, Lemmih <lemmih at gmail.com> wrote:
> We can make it a little faster by not doing bound checks:
> 
> > test4 :: IO ()
> > test4 = do
> >   (arr :: IOUArray Int Bool) <- newArray_ (0,100*100-1)
> >   doFromTo 0 9999 $ \_ ->
> >     doFromTo 0 99 $ \y ->
> >       doFromTo 0 99 $ \x ->
> >         unsafeWrite arr (x*(y+1)) False
> 
> Timings (compiled with -O2):
> test1: 12.6s
> test2: 8.5s
> test3: 1.9s
> test4: 1.3s

A small update making the test more fair:

> test5 :: IO ()
> test5 = do
>   (arr :: IOUArray Int Int) <- newArray_ (0,100*100-1)
>   doFromTo 0 9999 $ \_ ->
>     doFromTo 0 99 $ \y ->
>       doFromTo 0 99 $ \x ->
>         unsafeWrite arr (x*(y+1)) 0

I previously though that Bools were optimized away, guess I was wrong.
test5: 0.8s

-- 
Friendly,
  Lemmih