PHP 转 ASCII

<?php 
class ascii
{

function decode($str)
{
    preg_match_all( "/(d{2,5})/", $str,$a);
    $a = $a[0];
     foreach ($a as $dec)
     {
         if ($dec < 128)
         {
            $utf .= chr($dec);
         }
         else if ($dec < 2048)
        {
            $utf .= chr(192 + (($dec - ($dec % 64)) / 64));
            $utf .= chr(128 + ($dec % 64));
         }
         else
         {
            $utf .= chr(224 + (($dec - ($dec % 4096)) / 4096));
            $utf .= chr(128 + ((($dec % 4096) - ($dec % 64)) / 64));
            $utf .= chr(128 + ($dec % 64));
         }
     }
     return $utf;
}

function encode($c)
{
    $len = strlen($c);
    $a = 0;
     while ($a < $len)
     {
        $ud = 0;
         if (ord($c{$a}) >=0 && ord($c{$a})=192 && ord($c{$a})=224 && ord($c{$a})=240 && ord($c{$a})=248 && ord($c{$a})=252 && ord($c{$a})=254 && ord($c{$a}) encode("a");


?>