`include "../fig41-full-adder/adder.sim.v"
module MULTIPLE_INSTANCE (a, b, c, d, cin, cout, sum);
	localparam DATA_WIDTH = 4;

	input  wire [DATA_WIDTH-1:0] a;
	input  wire [DATA_WIDTH-1:0] b;
	input  wire [DATA_WIDTH-1:0] c;
	input  wire [DATA_WIDTH-1:0] d;
	output wire [DATA_WIDTH*2-1:0] sum;

	input  wire [DATA_WIDTH-1:0] cin;
	output wire [DATA_WIDTH-1:0] cout;

	wire [DATA_WIDTH-1:0] a2b;

	genvar i;
	/* n = 0..DATA_WIDTH
	 *
	 *       cin[n]
	 *        ↓
	 *   a[n] + b[n] → sum[n]
	 *        ↓
	 *   c[n] + d[n] → sum[4+n]
	 *        ↓
	 *      cout[n]
	 */
	for(i=0; i<DATA_WIDTH; i=i+1) begin
		ADDER comb_apb (.a(a[i]), .b(b[i]), .cin(cin[i]), .cout(a2b[i]),  .sum(sum[i]));
		ADDER comb_cpd (.a(c[i]), .b(d[i]), .cin(a2b[i]), .cout(cout[i]), .sum(sum[DATA_WIDTH+i]));
	end

endmodule