Arithmetic is where the answer is right and everything is nice and you can look out the window and see the blue sky-or the answer is wrong and you have to start all over and try again and see how it comes out this time.-Carl Sandberg
In this chapter we will examine arithmetic circuits as detailed case studies of the principles of combinational logic design. Up to this point, we have concentrated on circuits that manipulate binary numbers as unsigned magnitudes only. We begin this chapter looking at ways to represent both positive and negative numbers in the binary system, and at the various schemes for adding and subtracting signed numbers. Then we will revisit the circuits for the half and full adder, as these form the basis for just about every arithmetic circuit we will meet.