What is the primary function of an adder-subtractor in digital circuits?

The primary function of an adder-subtractor in digital circuits is to perform arithmetic operations, specifically addition and subtraction. An adder-subtractor circuit is designed to take two binary numbers as inputs and, depending on the mode it operates in, either add these numbers together or subtract one from the other.

In digital electronics, this dual functionality is essential for various applications where arithmetic calculations are required, such as in arithmetic logic units (ALUs) found in processors. These circuits typically utilize common components, such as full adders, and incorporate additional logic to handle the subtraction operation by utilizing techniques like two's complement representation.

This capability is foundational for many digital systems, where efficient and accurate calculations are necessary for data processing, computation, and control systems. The other options, while related to various aspects of digital circuitry, do not capture this specific functionality of performing arithmetic operations.