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