private static function _initializeMaps()
 {
     if (!isset(self::$_charMap)) {
         self::$_charMap = array();
         for ($byte = 0; $byte < 256; ++$byte) {
             self::$_charMap[$byte] = chr($byte);
         }
         self::$_byteMap = array_flip(self::$_charMap);
     }
 }