71. Arithmetic Logic Unit

How do you plan to solve it?

module alu4(
    input [3:0]a,b,
    input [2:0]op,
    output reg [3:0]y,
    output reg cf
);
reg carry,borrow;
always@(*)begin
    y=4'b0;
    cf=1'b0;
    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 : y = a & b;
        3'b011 : y = a | b;
        3'b100 : y = a ^ b;
        default: y = 4'b0000;
    
    endcase
end
endmodule