encode/decode string

function strcode($str, $passw = "", $encode = true) {
    if (!$encode) {
        $str = base64_decode($str);
    }
    $salt = "Dn8*#2n!9j";
    $len = strlen($str);
    $gamma = '';
    $n = $len>100 ? 8 : 2;
    while (strlen($gamma) < $len) {
        $gamma .= substr(pack('H*', sha1($passw.$gamma.$salt)), 0, $n);
    }
    $str = $str ^ $gamma;

    if ($encode) {
        $str = base64_encode($str);
    }
    return $str;
}

$txt = "test_string";
$txt = strcode($txt, 'mypassword', true);
echo $txt . PHP_EOL;

$txt = strcode($txt, 'mypassword', false);
echo $txt;