Simon Marlow simonmar at microsoft.com
Tue May 25 18:22:08 EDT 2004

On 25 May 2004 15:52, Daan Leijen wrote:

> Ok, here is a new "IntMap" module that might improve the
> performance of "lookup". Please, let's first test it before
> adding the changes to the real distribution.
> I have:
> 1) removed calls to "natFromInt" and "intFromNat". Supposedly,
>     they should expand to nothing but who knows...

These calls were being optimised away by GHC.  However, something else
wasn't: namely the value of maxBound::Word which is used by complement.
There's no substitue for actually looking at the code that GHC

> 2) I have commented out the guard that tests if the integer
> is in the tree at all. When a key is present, lookup will be
> faster -- if the key is not present, lookup might be slower.
> Simon, I would be interested to see how it performs with and
> without the comment (2) (line 269). If performance is better
> without the comment, it means that ghc is spending time doing
> intFromNat/natFromInt which means that we might improve matters
> by storing Nat's instead of Int's in the IntMap. (I don't know
> if such tweaking is worth the trouble though.)

I'll run your new code tomorrow and let you know the results.


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