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)
            2'b00: alu_op =4'b0001;
            2'b01: alu_op =4'b0010;
            2'b10: alu_op =4'b0100;
            2'b11: alu_op =4'b1000;
        default :alu_op = 4'b0000;
        endcase
    end
endmodule