Mathematical recreation ? The sake of complexifty ? (it's fun when you can't even understand your own question after reading the answers). Maybe you should ask Paul Bauman about his motivation. Nicolas 2011/6/18 Stéphane Ducasse <stephane.ducasse@inria.fr>:
Is there an interest for security or other points?
Stef
On Jun 16, 2011, at 12:38 PM, Sven Van Caekenberghe wrote:
Hi,
On Planet Smalltalk I read about this challenge: http://www.parcplace.net/list/vwnc-archive/1106/msg00080.html the goal being to optimize the current, naive Integer>>#factorial implementation.
I had some old Lisp code hanging around, implementing an algorithm that I once found somewhere, and I ported it to Smalltalk. I am sure there are faster solutions, but this one is twice as fast as the original while still being easy to understand and it has a useful, safe helper method:
Integer>>#svcFactorial    "Answer the factorial of the receiver."
   self = 0 ifTrue: [ ^ 1 ].    self > 0 ifTrue: [ ^ 1 productUpTo: self ].    self error: 'Not valid for negative integers'
Integer>>#productUpTo: anInteger    "Answer the product of all integers from the receiver (non-inclusive) up to anInteger (inclusive)."
   | difference split |    self assert: (self between: 0 and: anInteger).    "the idea is to multiply LargePositiveIntegers of approximately the same size"    difference := anInteger - self.    difference = 0 ifTrue: [ ^ 1 ].    difference = 1 ifTrue: [ ^ anInteger ].    difference = 2 ifTrue: [ ^ (anInteger - 1) * anInteger ].    difference = 3 ifTrue: [ ^ (anInteger - 2) * (anInteger - 1) * anInteger ].    difference = 4 ifTrue: [ ^ (anInteger - 3) * (anInteger - 2) * (anInteger - 1) * anInteger ].    split := (self + anInteger) bitShift: -1.    ^ (self productUpTo: split) * (split productUpTo: anInteger)
Would it be a good idea to replace the current implementation with this one ?
Sven