71. Arithmetic Logic Unit

How do you plan to solve it?

module alu4(
    input [3:0] a,
    input [3:0] b,
    input [2:0] op,
    output reg [3:0] y,
    output reg cf
);

always @(*) begin
    case (op)
        3'b000: begin {cf, y} <= a + b; end
        3'b001: begin {cf, y} <= a - b; end
        3'b010: begin y <= a & b; cf <= 0; end
        3'b011: begin y <= a | b; cf <= 0; end
        3'b100: begin y <= a ^ b; cf <= 0; end
        default: begin y = 4'b0000; cf = 0; end
    endcase
end

endmodule