Prime Tests

README.md

1048576 should be around 30 seconds for ruby 1.9.3p327

prime.rb

def highest_divisor(i)
  j = 2
  while j <= Math.sqrt(i.to_f).ceil
    if i % j == 0
      return j
    end
    j += 1
  end
  return -1
end

def is_prime(i)
  return true if i < 4
  return highest_divisor(i) == -1
end


started = Time.now
num = (ARGV.first || 1000000).to_i
cnt = 0
num.times do |i|
  if is_prime(i)
    cnt += 1 
  end
end
diff = Time.now - started

puts "%s\t%d\t%d\t%0.3f" % [RUBY_DESCRIPTION.split(" ", 3)[0,2].join("-"), num, cnt, diff]