71. Arithmetic Logic Unit

How do you plan to solve it?

module alu4(a,b,op,y,cf);
input [3:0] a,b;
input [2:0] op;
output reg [3:0] y;
output reg cf;
always @ (*) begin
    cf=0;
    y=0;
    case(op)
    3'b000: {cf,y}=a+b;
    3'b001: {cf,y}=a-b;
    3'b010: y=a&b;
    3'b011: y=a|b;
    3'b100: y=a^b;
    default : begin
        y=4'b0;
        cf=0;
    end
    endcase
end
endmodule