用于解析通过JS的escape函数加密过的数据

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;
}