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 cf , 
output reg [3:0]y );

always @(*) begin
    y = 16'b0;
    cf = 1'b0;
    case(op)
    3'b000 : {cf , y} = a + b;
    3'b001 :  {cf , y} = a +(~b + 1'b1);
    3'b010  : y = a & b  ;
    3'b011 : y = a | b;
    3'b100  : y = a ^ b;
   default :  y = 4'b0000 ;

    endcase


end
endmodule