51. Opcode Decoder

How do you plan to solve it?

module alu_decoder (
    input  [1:0] opcode,
    output reg [3:0] alu_op
);
    always @* begin
        case (opcode)
        0: alu_op= 4'b0001;
        1: alu_op= 4'b0010;
        2: alu_op= 4'b0100;
        3: alu_op= 4'b1000;
        endcase
    end
endmodule