实现PHP转ASCII

=0 && ord($c{$a})<=127)         {            $ud = ord($c{$a});            $a += 1;         }         else if (ord($c{$a}) >=192 && ord($c{$a})<=223)         {            $ud = (ord($c{$a})-192)*64 + (ord($c{$a+1})-128);            $a += 2;         }         else if (ord($c{$a}) >=224 && ord($c{$a})<=239)         {            $ud = (ord($c{$a})-224)*4096 + (ord($c{$a+1})-128)*64 + (ord($c{$a+2})-128);            $a += 3;         }         else if (ord($c{$a}) >=240 && ord($c{$a})<=247)         {            $ud = (ord($c{$a})-240)*262144 + (ord($c{$a+1})-128)*4096 + (ord($c{$a+2})-128)*64 + (ord($c{$a+3})-128);            $a += 4;         }         else if (ord($c{$a}) >=248 && ord($c{$a})<=251)         {            $ud = (ord($c{$a})-248)*16777216 + (ord($c{$a+1})-128)*262144 + (ord($c{$a+2})-128)*4096 + (ord($c{$a+3})-128)*64 + (ord($c{$a+4})-128);            $a += 5;         }         else if (ord($c{$a}) >=252 && ord($c{$a})<=253)         {            $ud = (ord($c{$a})-252)*1073741824 + (ord($c{$a+1})-128)*16777216 + (ord($c{$a+2})-128)*262144 + (ord($c{$a+3})-128)*4096 + (ord($c{$a+4})-128)*64 + (ord($c{$a+5})-128);            $a += 6;         }         else if (ord($c{$a}) >=254 && ord($c{$a})<=255)         { //error            $ud = false;         }        $scill .= "&#$ud;";     }     return $scill;}}/*PHP 转 ASCIIrequire_once "ascii_class.php";*/$aa = new ascii;echo $aa -> encode("a");?>