Example methods for converting Integers to and from bases over 36

convert_base.rb

#!/usr/bin/env ruby -wKU

B64_ALPHABET = ('0'..'9').to_a + ('a'..'z').to_a + ('A'..'Z').to_a + ['+', '/']

class Integer
  def to_s64( base = 64 )
    input = self
    out = ""
    while input > 0
      digit = input % base
      out = B64_ALPHABET[digit] + out
      input = (input - digit) / base
    end
    out
  end
end

class String
  def to_i64( base = 64 )
    result = 0
    self.each_byte do |char|
      value = B64_ALPHABET.index(char.chr)

      if value.nil? or value >= base then
        return result
      end
    
      result *= base
      result += value
    end
    return result
  end  
end

if $0 == __FILE__
  p = [2, 5, 13, 64, 128, 255]

  p.each do |x|
    s = x.to_s64(52)
    i = s.to_i64(52)
    puts "#{x} == #{s} == #{i}"
  end
end