// 4.34: parameterized multiplexer

module mux2
  #(parameter width = 8)
   (input  logic [width-1:0] d0, d1, 
    input  logic             s,
    output logic [width-1:0] y);

   assign y = s ? d1 : d0; 
endmodule

module mux4(input  logic [11:0] d0, d1, d2, d3,
            input  logic [1:0]  s,
            output logic [11:0] y);

  logic [11:0] low, hi;

  mux2 #(12) lowmux(d0, d1, s[0], low);
  mux2 #(12) himux(d2, d3, s[1], hi);
  mux2 #(12) outmux(low, hi, s[1], y);
endmodule