Chris,

> Even with a few collisions, I'm perplexed why removing 2001 
> keys takes **5 hours**..!

A few collisions?! I don't think so ;-) Let's do a little math:

Dictionaries use linear searches in order to fix the collision chains.
Your objects had hashes ranging from h to h+256. You added roughly 2K
objects to the dictionary. Let's look:

* the first 256 adds had no collisions
* the next 256 adds had collision chains of approx. length 128
* the next 256 adds had collision chains of approx. length 384
...
So on average we have (after adding 2K objects) a collision chain of
length 1000 for each object (very rough estimation).

Collision fixing does the following: It traverses the collision chain
for the object being removed and finds the new position for each object
in the chain. Meaning that we have 1000 loops (traversing the collision
chain) of 1000 operations (finding new index for object in collision
chain - which will naturally also traverse any existing collision chain
up to the end). Meaning we got roughly 1,000,000 comparisons for
removing a single object.

Do this 2000 times and you end up with

	2,000,000,000 large integer comparisons.

That *may* take a little, right?! ;-)


>   ^self bitAnd: 16r3FFFFFFF

I think that's the right solution.

Cheers,
  - Andreas