On 16.12.2011 00:40, Henrik Sperre Johansen wrote:
On 15.12.2011 23:35, Mariano Martinez Peck wrote:
Well...it is much slower :( it seems that the cost of (aKey
identityHash + ( aKey mareaClass identityHash bitShift: 12) + (aKey
basicSize bitShift: 24)
is bigger than the colisions.
Anyway, thanks for the nice thread. I learned.
Cheers
Well, first of all, that always creates a largeInteger, since
identityHash is already shifted by 22... You'd want to be using
basicIdentityHash.
2nd off, basicSize is useless for non-variable classes, which I guess
is the common case.
3rd, putting class hash in the high bits won't really help much if
you're serializing many instances of the same class, as they will all
occupy a sequential hash range.
So if I were you, I'd try with something like
obj basicIdentityHash << 12 + (obj class basicIdentityHash)
before discarding it outright due to computation cost.
Cheers,
Henry
A few more points:
1) don't use PluggableSets. Block activations are costly, and you REALLY
need specialized data/hash functions for it to be worth using.
2) Even with a subclass of IdentitySet, it's hardly worth it:
PluggableSet:
n := 1000000.
set := PluggableSet new: n.
set hashBlock: [:obj | obj basicIdentityHash << 12 + (obj class
basicIdentityHash) ].
set equalBlock: [ :a :b | a == b ].
Time millisecondsToRun: [1 to: n do: [:waste | set add: Object new.]] 18828
The one I suggested in a custom subclass:
n := 1000000.
set := PseudoIdentitySet new: n.
Time millisecondsToRun: [1 to: n do: [:waste | set add: Object new.]]
14182
Usual identitySet:
n := 1000000.
set := IdentitySet new: n.
Time millisecondsToRun: [1 to: n do: [:waste | set add: Object new.]] 4595
Custom subclass with a slightly modified hash (anObject identityHash +
(anObject class basicIdentityHash bitShift: 6)):
n := 1000000.
set := PseudoIdentitySet2 new: n.
Time millisecondsToRun: [1 to: n do: [:waste | set add: Object new.]] 3694
Why 6 you ask? Because I'm worth it.
Not really enough to justify the extra compexity, imho.
Cheers,
Henry
