function urshift($x, $n){
    $mask = 0x40000000;
    if ($x < 0){
        $x &= 0x7FFFFFFF;
        $mask = $mask >> ($n-1);
        $ret = ($x >> $n) | $mask;
        $ret = str_pad(decbin($ret), 32, '0', STR_PAD_LEFT);
        $ret[0] = '1';
        $ret = bindec($ret);
    } else {
            $ret = (int)$x >> (int)$n;
    }
    return $ret;