def decode_map
        @decode_map ||= replace_separator_decode({
          '1' =>  '0', '2' =>  '1', '3' =>  '2', '4' =>  '3', '5' =>  '4', '6' =>  '5', '7' =>  '6', '8' =>  '7', '9' =>  '8', '0' =>  '9',
          '-' => '10', '=' => '11', '!' => '12', '@' => '13', '#' => '14', '$' => '15', '%' => '16', '^' => '17', '&' => '18', '*' => '19',
          '(' => '20', ')' => '21', '_' => '22', '+' => '23', 'a' => '24', 'b' => '25', 'c' => '26', 'd' => '27', 'e' => '28', 'f' => '29',