playing with a prime number seive in ruby

primes.rb

# http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
 class Primes

  def self.time_it
    t = Time.now
    rval = yield
    elapsed = Time.now - t 
    #return rval, elapsed
    puts elapsed
    return rval
  end 

  def self.detect_primes(primes, limit);
    time_it do
      last = primes.last + 1 
      (last..limit).each do |number|
        primes << number unless primes.any? { |prime| number % prime == 0}
      end 
      primes
    end 
  end 

  def self.detect_primes2(primes, limit)
    time_it do
      last = primes.last + 1 
      cache = Hash.new { |hsh,key| hsh[key] = key ** 2 } 
      (last..limit).each do |number|
        primes << number unless primes.select { |p| cache[p] <= number }.any? { |prime| number % prime == 0 } 
      end 
      primes
    end 
  end 

  def self.detect_primes3(primes, limit)
    time_it do
      last = primes.last + 1 
      (last..limit).each do |number|
        primes << number unless primes.select { |p| p**2 <= number }.any? { |prime| number % prime == 0 } 
      end 
      primes
    end 
  end 

  def self.detect_primes4(primes, limit)
    time_it do
      last = primes.last + 1 
      (last..limit).each do |number|
        num_sq = number ** 0.5 
        primes << number unless primes.select { |p| p <= num_sq }.any? { |prime| number % prime == 0 } 
      end 
      primes
    end 
  end 

  def self.detect_primes5(primes, limit)
    time_it do
      searchable_primes = primes.clone
      last_searchable_prime_squared = searchable_primes.last ** 2
      last = primes.last + 1 
      (last..limit).each do |number|
        if last_searchable_prime_squared <= number
          searchable_primes << primes[searchable_primes.size]
          last_searchable_prime_squared = searchable_primes.last ** 2
        end 
        primes << number unless searchable_primes.any? { |prime| number % prime == 0 } 
      end 
      primes
    end 
  end 

end

#max = 50_000
#puts primes = Primes.detect_primes([2], max).count
#Primes.detect_primes2([2], max)
#Primes.detect_primes3([2], max)
#puts Primes.detect_primes4([2], max).count
#puts Primes.detect_primes4([2], max).count
#
primes = Primes.detect_primes([2], 2**16)
puts #{primes.count} primes found"
logs = primes.map {|p| Math.log(p,2) }.
puts logs.inject(Hash.new(0)) {|memo, log| memo[log.floor] += 1; memo}.sort.inspect
stuff.each_cons(2) {|(a,b),(c,d)| puts "primes log base 2 range: #{a}-#{c}, count: #{b}-#{d}, count_ratio: #{(d/b.to_f).round(2)}" }

change to PrimeTime and change inputs hehehe!

i wonder about building my own recursive square root finder that goes to the nearest integer instead of the one that exists...