4-bit adder/subtractor X42916

Design a circuit that performs the addition or subtraction of two 4-bit numbers. The result (mod 16) must be represented in 4 bits also. The circuit has an input (op) that indicates which operation must be performed (0 for addition, 1 for subtraction).
Specification

module add_sub4(a, b, op, result); input [3:0] a, b; input op; output [3:0] result;

Input

• a and b are the two 4-bit operands.
• op indicates the type of operation (0 for addition, 1 for subtraction).

Output

• result is the 4-bit result of the operation (mod 16).