87. 4-bit Bidirectional Shift Register

How do you plan to solve it?

module shift_reg_bidirectional (
    input        CLK,
    input        RST,
    input        DIR,
    input        serial_in,
    output reg [3:0] Q
);
    always @(posedge CLK) begin
        if (RST) begin
            Q <= 4'b0000;
        end else if (DIR) begin
            //shift_left
            Q <= {Q[2:0], serial_in};
        end else begin
            //shift_right
            Q <= {serial_in, Q[3:1]};
        end
    end
endmodule