Implementation method of escape decoding function under PHP_PHP tutorial

function unescape($str) {
$str = rawurldecode( $str);
preg_match_all("/%u.{4}|.{4};|d+;|.+/U",$str,$r);
$ar = $r[0];
foreach($ar as $k=>$v) {
if(substr($v,0,2) == "%u")
$ar [$k] = iconv("UCS-2","GBK",pack("H4",substr($v,-4)));
elseif(substr($v,0,3) == "")
$ar[$k] = iconv("UCS-2","GBK",pack("H4",substr($v,3,-1)));
elseif(substr($v,0,2) == "") {
$ar[$k] = iconv("UCS-2","GBK",pack("n",substr($ v,2,-1)));
}
}
return join("",$ar);
}

function unescape($str){
$ret = '';
$len = strlen($str);
for ($i = 0; $i < $len; $i++){
if ($str[$i] == '%' && $str[$i +1] == 'u'){
$val = hexdec(substr($str, $i+2, 4));
if ($val < 0x7f) $ret .= chr($ val);
else if($val < 0x800) $ret .= chr(0xc0|($val>>6)).chr(0x80|($val&0x3f));
else $ret . = chr(0xe0|($val>>12)).chr(0x80|(($val>>6)&0x3f)).chr(0x80|($val&0x3f));
$i += 5 ;
}
else if ($str[$i] == '%'){
$ret .= urldecode(substr($str, $i, 3));
$i += 2;
}
else $ret .= $str[$i];
}
return $ret;
}