base62.rb

class Base62
  BASE62_ALPHABET = ('0'..'9').to_a + ('a'..'z').to_a + ('A'..'Z').to_a

  def encode(str)
    packed_int = str.unpack('C*').each_with_index.reduce(0){|r,(x,i)| r + (x << 8*i) }

    return '0' if packed_int == 0
    s = ''

    while packed_int > 0
      s << BASE62_ALPHABET[packed_int.modulo(62)]
      packed_int /= 62
    end
    s.reverse
  end
end