71. Arithmetic Logic Unit

How do you plan to solve it?

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

parameter [2:0]ADD = 0,SUB = 1,AND = 2,OR = 3,XOR = 4;
// reg carry;
// reg [3:0] temp;

always @(*) begin
    y = 4'b0000;
    cf = 1'b0;
    // carry = 1'b0;
    case(op)
    ADD : {cf,y} = a + b;
    SUB : begin
        {cf,y} = a + ~b + 1;
        // cf = ~carry;
    end
    AND : begin
        y = a & b;
        cf = 0;
    end
    OR : begin
        y = a | b;
        cf = 0;
    end
    XOR : begin
        y = a ^ b;
        cf = 0;
    end
    default : begin
        y = 0;
        cf = 0;
    end
    endcase
end

// assign cf = op == SUB ? ~carry : carry;
// assign y = temp;

endmodule