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
);
    // Write your code here
    always @(posedge CLK or posedge RST) begin
        if(RST==1'b1) begin
            Q<=4'b0000;
        end
        else if(DIR==1'b1) begin
            Q<={Q[2:0],serial_in};
        end
        else if(DIR==1'b0) begin
            Q<={serial_in,Q[3:1]};
        end
    end
endmodule