/**
* @inheritDoc
*/
public function getSignal()
{
$signal = parent::getSignal();
if (is_null($signal)) {
$input = $this->source->getSignal();
if (!is_null($input)) {
$signal = SixteenBitMask::mask(~$input);
$this->setSignal($signal);
}
}
return $signal;
}
