3.2.1 TWO’S COMPLEMENT ADDITION AND SUBTRACTION
In this section, we look at the addition of signed two’s complement numbers. As we explore the addition of signed numbers, we also implicitly cover subtraction as well, as a result of the arithmetic principle:
a - b = a + (−b).
We can negate a number by complementing it (and adding 1, for two’s complement), and so we can perform subtraction by complementing and adding. This results in a savings of hardware because it avoids the need for a hardware subtractor. We will cover this topic in more detail later. We will need to modify the interpretation that we place on the results of addition when we add two’s complement numbers.