bool isPositionRequest( std::uint8_t formatSpecifier, std::uint8_t category, std::uint8_t natureOfDistressOfTelecommand1, std::uint8_t typeOfCommunicationOrTelecommand2 )
{
    return formatSpecifier == FormatSpecifierIndividualStations
        && category == CategorySafety
        && ( natureOfDistressOfTelecommand1 == FirstTelecommandInvalid || natureOfDistressOfTelecommand1 == FirstTelecommandShipPositionOrLocationRegistrationUpdating )
        && ( typeOfCommunicationOrTelecommand2 == SecondTelecommandInvalid || typeOfCommunicationOrTelecommand2 == SecondTelecommandNoInformation );
}

MMSI mmsi;
if ( DSCTarget::isPositionRequest( formatSpecifier, category, natureOfDistressOr1stTelecommand, subseqComModeOr2ndTelecommand ) )
{
    mmsi = address; // mmsi is taken from field 2 of DSC
}
else
{
    mmsi = mmsiOfShipInDistress; // mmsi is taken from field 8 of DSC
}