php解密javascript's escape函数

<script>
	document.write(escape('开源中国社区'));
</script>

<?php	
function js_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;
}

$string = '%u5F00%u6E90%u4E2D%u56FD%u793E%u533A';
echo js_unescape($string);
?>