Prime.rb

class Prime
	def Prime.within from, to, priorPrimes=[]
		if from>2 and priorPrimes==[]
			priorPrimes = Prime.within 2, from-1
		end

		# update the table with previous prime
		table = Hash.new(true)
		priorPrimes.each {|prime|
			newFrom = [(from/prime.to_f).ceil*prime, prime*prime].max
			newFrom.step(to, prime) {|num| table[num] = false}
		}

		# generate primes in [from, to]
		primes = []
		prime = [from, 2].max
		while true
			prime += 1 until table[prime]==true
			break if prime>to

			primes.push prime
			table[prime] = false
			(prime*prime).step(to, prime) {|num| table[num] = false}
		end

		primes
	end

	def Prime.upto max
		(Prime.within 2, max).each {|prime| yield prime}
	end

	def Prime.firstFew amount
		primes = []
		blockFrom = 2
		blockTo = 1024

		begin
			primes += Prime.within blockFrom, blockTo, primes
			blockFrom = blockTo+1
			blockTo = primes.last*primes.last
		end while primes.length<amount

		primes[0...amount]
	end
end