It would be useful to have one or more overloads of this helper function, in the form of either or both of the following:-

quint16 qChecksum (const QByteArray& data ){
return qChecksum( data.constData(), data->count() );
}
or

quint16 qChecksum (const QByteArray &data, uint len ){
return qChecksum( data.constData(), len );
}