Based on work done by Tantek Çelik: http://ttk.me/w/NewBase60 | http://ttk.me/w/NewBase64

BaseConvert.rb

class BaseConvert

  CHARS = "0123456789ABCDEFGHJKLMNPQRSTUVWXYZ_abcdefghijkmnopqrstuvwxyz" # !-+*$
  BASE  = CHARS.length

  def self.num_to_str(num = nil)
    str = ""
    
    return 0 if num.nil? || num.zero?
   
    while num > 0 do
      mod = num % BASE
      str = CHARS[mod, 1] + str
      num = (num - mod) / BASE
    end
   
    str
  end

  def self.str_to_num(string)
    num = 0
    
    string.each_byte do |char|
      case char
        when 33, 73, 108  then char  = 1  # typo capital I, lowercase l, ! to 1
        when 36           then char  = 63 # dollar sign
        when 42           then char  = 62 # asterisk
        when 44           then char  = 61 # plus
        when 45           then char  = 60 # dash
        when 48..57       then char -= 48
        when 65..72       then char -= 55
        when 74..78       then char -= 56
        when 79           then char  = 0  # error correct typo capital O to 0
        when 80..90       then char -= 57
        when 95           then char  = 34 # underscore
        when 97..107      then char -= 62
        when 109..122     then char -= 63
        else                   char  = 0  # treat all other noise as 0
      end

      num = BASE * num + char
    end

    num
  end

  class << self
    alias_method :encode, :num_to_str
    alias_method :decode, :str_to_num
  end

end