Simple Gödel encoding and decoding

godel.rb

#!/usr/bin/env ruby
# encoding: UTF-8
#
# Simple Gödel encoding
# Ruby 1.9.3

require 'prime'

# Allowed characters
CHARS = ' ABCDEFGHIJKLMNOPQRSTUVWXYZ'

def decode(encoded)
  decoded = ''
  primes = Prime::EratosthenesGenerator.new
  while !decoded.match('  ')
    prime = primes.next
    temp = encoded
    pow = 0
    while (temp % prime) == 0
      temp = temp / prime
      pow += 1
    end
    decoded << CHARS[pow]
  end
  return decoded.strip
end

def encode(plaintext)
  encoded = 1
  primes = Prime::EratosthenesGenerator.new
  i = 0
  # Ensure no double-spaces in source text, as that 
  # indicates message termination when decoding
  text = plaintext.gsub(/  */, ' ').upcase
  text.each_char do |x|
    c = CHARS.index(x)
    if c
      i += 1
      encoded = encoded * primes.next**c
    end
  end
  return encoded
end

puts encode('All work and no play makes Jack a dull boy')
puts decode(302841943913193385738713551625817000427562261942842587929015537746428183661378187315559771978420129418887436160028297029588657156437015075648670687785809963529258353218547333325583147736258864907770101429735906490566082415554531521796426549706253542076864961225050164062500000000000)