Levente Uzonyi uploaded a new version of Kernel to project The Trunk:
http://source.squeak.org/trunk/Kernel-ul.597.mcz

==================== Summary ====================

Name: Kernel-ul.597
Author: ul
Time: 17 June 2011, 12:38:04.174 am
UUID: 579dc488-9b22-5f4c-8a32-d60e5a1f2032
Ancestors: Kernel-ul.596

A more efficient implementation of Integer class >> #primesUpTo:do: using the Sieve of Eratosthenes.

=============== Diff against Kernel-ul.596 ===============

Item was changed:
  ----- Method: Integer class>>primesUpTo:do: (in category 'prime numbers') -----
  primesUpTo: max do: aBlock
  	"Compute aBlock with all prime integers up to the given integer."
  	"Integer primesUpTo: 100"
  
+ 	| index limit limitSqrtFloor sieve |
+ 	limit := max asInteger.
+ 	limit <= 1 ifTrue: [ ^self ].
- 	| limit flags prime k |
- 	limit := max asInteger - 1.
  	"Fall back into #largePrimesUpTo:do: if we'd require more than 100k of memory; 
  	the alternative will only requre 1/154th of the amount we need here and is almost as fast."
+ 	limit > 25000 ifTrue:[ ^self largePrimesUpTo: limit do: aBlock ].
+ 	limit := limit - 1. "upTo:"
+ 	sieve := Array new: limit withAll: true.
+ 	sieve at: 1 put: false.
+ 	index := 2.
+ 	limitSqrtFloor := limit sqrtFloor.
+ 	[ index <= limitSqrtFloor ] whileTrue: [
+ 		(sieve at: index) ifTrue: [
+ 			| notPrimeIndex |
+ 			aBlock value: index.
+ 			notPrimeIndex := index * index.
+ 			[ notPrimeIndex <= limit ] whileTrue: [
+ 				sieve at: notPrimeIndex put: false.
+ 				notPrimeIndex := notPrimeIndex + index ] ].
+ 		index := index + 1 ].
+ 	[ index <= limit ] whileTrue: [
+ 		(sieve at: index) ifTrue: [
+ 			aBlock value: index ].
+ 		index := index + 1 ]
+ 	!
- 	limit > 25000 ifTrue:[^self largePrimesUpTo: max do: aBlock].
- 	flags := (Array new: limit) atAllPut: true.
- 	1 to: limit - 1 do: [:i |
- 		(flags at: i) ifTrue: [
- 			prime := i + 1.
- 			k := i + prime.
- 			[k <= limit] whileTrue: [
- 				flags at: k put: false.
- 				k := k + prime].
- 			aBlock value: prime]].
- !