chischaschos-primes.rb

require 'ruby-prof'

def prime(n)
  limit = n
  numbers = Array.new(n + 1) { true }
  start = 2
  primes = []

  loop do
    numbers[start] && primes << start
    cross_multiples start, numbers
    start = next_bigger_than start, numbers
    start > limit && break
  end

  primes
end

def cross_multiples number, numbers
  next_to_cross = number + number

  loop do
    numbers[next_to_cross].nil? && break
    numbers[next_to_cross] && numbers[next_to_cross] = false
    next_to_cross += number
  end
end

def next_bigger_than number, numbers
  increment = 1
  next_bigger = number + increment

  loop do
    if numbers[next_bigger] || numbers[next_bigger].nil?
      break
    else
      next_bigger += 1
    end
  end

  next_bigger
end

RubyProf.start
p prime 1_000_000
result = RubyProf.stop

printer = RubyProf::FlatPrinter.new result
printer.print STDOUT

output

➜  katas  ruby primes.rb
Thread ID: 70312662476500
Fiber ID: 70312668298920
Total: 16.014233
Sort by: self_time

 %self      total      self      wait     child     calls  name
 16.57      2.654     2.654     0.000     0.000  3696711   Kernel#nil?
  3.88      0.621     0.621     0.000     0.000        1   Array#initialize
  3.44      0.550     0.550     0.000     0.000   921501   Array#[]=
  3.12     15.393     0.500     0.000    14.893   156997  *Kernel#loop
  2.68      4.218     0.429     0.000     3.789    78498   Object#next_bigger_than
  1.86     10.675     0.298     0.000    10.377    78498   Object#cross_multiples
  0.60      0.097     0.097     0.000     0.000    78499   NilClass#nil?
  0.00     16.014     0.000     0.000    16.014        1   Global#[No method]
  0.00     16.014     0.000     0.000    16.014        1   Object#prime
  0.00      0.621     0.000     0.000     0.621        1   Class#new

* indicates recursively called methods