<P> that has control input D (\ displaystyle D) that is also connected to the initial carry, then the modified adder performs </P> <Ul> <Li> addition when D = 0 (\ displaystyle D = 0), or </Li> <Li> subtraction when D = 1 (\ displaystyle D = 1). </Li> </Ul> <Li> addition when D = 0 (\ displaystyle D = 0), or </Li> <Li> subtraction when D = 1 (\ displaystyle D = 1). </Li>

The combination of which gates/ circuits is used to implement adder-subtractor