compute_primes

# File lib/prime.rb, line 438
    def compute_primes
      # max_segment_size must be an even number
      max_segment_size = 1e6.to_i
      max_cached_prime = @primes.last
      # do not double count primes if #compute_primes is interrupted
      # by Timeout.timeout
      @max_checked = max_cached_prime + 1 if max_cached_prime > @max_checked

      segment_min = @max_checked
      segment_max = [segment_min + max_segment_size, max_cached_prime * 2].min
      root = Integer.sqrt(segment_max)

      segment = ((segment_min + 1) .. segment_max).step(2).to_a

      (1..Float::INFINITY).each do |sieving|
        prime = @primes[sieving]
        break if prime > root
        composite_index = (-(segment_min + 1 + prime) / 2) % prime
        while composite_index < segment.size do
          segment[composite_index] = nil
          composite_index += prime
        end
      end

      @primes.concat(segment.compact!)

      @max_checked = segment_max
    end