71. Arithmetic Logic Unit

How do you plan to solve it?

/*Write your code here*/
module alu4( input [3:0] a,
             input [3:0]b,
             input  [2:0] op,
             output reg [3:0]  y,
             output reg cf);
    reg carry;
    reg borrow;

    always@(*)
    case(op)
    3'b000: begin
                {carry,y }= a+ b;
                cf = carry;
    end
    3'b001: begin
           {borrow, y} = a + ~b +1;
            cf = borrow;
    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


endmodule