On Dec 17, 2007 1:49 PM, Bert Freudenberg <bert at freudenbergs.de> wrote:
> > 0 bitXnor: 0 -> -1
>
> And what exactly is wrong with that?
>
err... I'd expect '1' here? The problem is that bitInvert is not
identical, as far as I can tell, with bitNot...

1 bitInvert -> -2

(where '1 bitNot' should result in 0)

And for the problem itself: drawing a quick list of truth tables of
available bit ops quickly pointed out that counting similar bits with
XNOR and counting different bits with XOR are equivalent ;-P. That's
what you get for firing off posts at the end of your lunch break.
Making the number of matching bits a similarity indicated based on the
length of the largest bit string, I currently have (pending more unit
tests ;-)):

findSimilarityBetween: n1 and: n2
	"check how similar n1 and n2 are. Similarity is defined of the maximum
	 matching number of bits - if n1 << n2, we'll 'slide' n1 along n2'''"
	
	| small large match thisMatch thisMatchBitcount nBits |
	
	(n1 = n2) ifTrue: [^1.0].
		
	(n1 < n2)
		ifTrue: [small := n1. large := n2]
		ifFalse: [small := n2. large := n1].
	match := 0.
	nBits := large highBitOfMagnitude.
	
	1 to: nBits do: [:i |
		thisMatch := small bitXor: large.
		thisMatchBitcount := nBits - (self countBits: thisMatch).
		(thisMatchBitcount > match)
			ifTrue: [match := thisMatchBitcount].
		small := small << 1].
	
	^match / (nBits * 1.0)






-- 
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universe so full of wonders, they have managed to invent boredom. " -
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