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sieve of eratosthenes

Smalltalk

" Sieve of Erastosthenes in Smalltalk (GNU Smalltalk)
  Written by Rob Hoelz

  To run:
    gst sieve.st -a <limit>
"

Object subclass: #Sieve
    instanceVariableNames: 'primes'
    classVariableNames: ''
    poolDictionaries: ''
    category: nil.

!Sieve class methodsFor: 'instance creation'!

new: limit
    |r|

    r := super new.
    r init: limit.
    ^r
! !

!Sieve methodsFor: 'instance initialization'!
init: limit
    primes := Array new: limit.
    primes at: 1 put: 0.
    2 to: limit do: [:x| primes at: x put: 1]
! !

!Sieve methodsFor: 'prime generation'!
generate
    |currPrime|

    currPrime := 2.
    [((currPrime * currPrime) <= (primes size))] whileTrue: [self removeMultiples: currPrime. currPrime := self nextPrime: currPrime]
! !

!Sieve methodsFor: 'printing'!
printPrimes
    |index|

    index := 1.
    primes do: [:x| (x = 1) ifTrue: [Transcript show: (index displayString). Transcript show: ' ']. index := index + 1].
    Transcript cr
! !

!Sieve methodsFor: 'private'!
removeMultiples: currPrime
    |index|

    index := currPrime * 2.
    [(index <= (primes size))] whileTrue: [primes at: index put: 0. index := index + currPrime]
!
nextPrime: currPrime
    |index|

    index := currPrime + 1.
    [(index <= (primes size))] whileTrue: [(1 = (primes at: index)) ifTrue: [^index]. index := index + 1].
    ^(primes size)
! !

|argv limit s|
argv := Smalltalk arguments.
limit := (argv at: 1) asInteger.
s := Sieve new: limit.
s generate.
s printPrimes.

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