+---+ +---+ | X | | Y | +---+ +---+ | | ---->XOR<---- --------| | \ / | +---+ | | R | | +---+ | | | \ / | P rowwise | | | \ / | +---+ | | Q | | +---+ | | | \ / | P columnwise | | | \ / | +---+ | | Z | | +---+ | | | \ / ------>XOR | \ /