short.rb

  CHARS = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
  SIZE = CHARS.size
  def short(number)
    chars = []
    while number != 0 do
      number, mod = number.divmod(SIZE)
      chars.unshift(CHARS[mod])
    end
    chars.pack('c' * chars.size)
  end