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+
+// Via http://www.edaplayground.com/s/6/591
+// stackoverflow 20556634
+// http://stackoverflow.com/questions/20556634/how-can-i-iteratively-create-buses-of-parameterized-size-to-connect-modules-also
+
+// Code your design here
+`define macro_args
+`define indexed_part_select
+
+module Multiplier_flat #(parameter M = 4, parameter N = 4)(
+input [M-1:0] A, //Input A, size M
+input [N-1:0] B, //Input B, size N
+output [M+N-1:0] P ); //Output P (product), size M+N
+
+/* Calculate LSB using Wolfram Alpha
+ N==3 : http://www.wolframalpha.com/input/?i=0%2C+4%2C+9%2C+15%2C+...
+ N==4 : http://www.wolframalpha.com/input/?i=0%2C+5%2C+11%2C+18%2C+26%2C+35%2C+...
+ N==5 : http://www.wolframalpha.com/input/?i=0%2C+6%2C+13%2C+21%2C+30%2C+...
+ */
+`ifdef macro_args
+// initial $display("Use Macro Args");
+`define calc_pp_lsb(n) (((n)-1)*((n)+2*M)/2)
+//`define calc_pp_msb(n) (`calc_pp_lsb(n+1)-1)
+`define calc_pp_msb(n) ((n**2+(2*M+1)*n-2)/2)
+//`define calc_range(n) `calc_pp_msb(n):`calc_pp_lsb(n)
+`define calc_pp_range(n) `calc_pp_lsb(n) +: (M+n)
+
+wire [`calc_pp_msb(N):0] PP;
+assign PP[`calc_pp_range(1)] = { 1'b0 , { A & {M{B[0]}} } };
+assign P = PP[`calc_pp_range(N)];
+`elsif indexed_part_select
+// initial $display("Use Indexed Part Select");
+localparam MSB = (N**2+(2*M+1)*N-2)/2;
+wire [MSB:0] PP;
+assign PP[M:0] = { 1'b0 , { A & {M{B[0]}} } };
+assign P = PP[MSB -: M+N];
+`else
+// initial $display("Use Worst Case");
+localparam MSB = (N**2+(2*M+1)*N-2)/2;
+wire [MSB:0] PP;
+assign PP[M:0] = { 1'b0 , { A & {M{B[0]}} } };
+assign P = PP[MSB : MSB+1-M-N];
+`endif
+
+genvar i;
+generate
+for (i=1; i < N; i=i+1)
+begin: addPartialProduct
+ wire [M+i-1:0] gA,gB,gS;
+ wire Cout;
+ assign gA = { A & {M{B[i]}} , {i{1'b0}} };
+ `ifdef macro_args
+ assign gB = PP[`calc_pp_range(i)];
+ assign PP[`calc_pp_range(i+1)] = {Cout,gS};
+ `elsif indexed_part_select
+ assign gB = PP[(i-1)*(i+2*M)/2 +: M+i];
+ assign PP[i*((i+1)+2*M)/2 +: M+i+1] = {Cout,gS};
+ `else
+ localparam LSB = (i-1)*(i+2*M)/2;
+ localparam MSB = (i**2+(2*M+1)*i-2)/2;
+ localparam MSB2 = ((i+1)**2+(2*M+1)*(i+1)-2)/2;
+ assign gB = PP[MSB : LSB];
+ assign PP[ MSB2 : MSB+1] = {Cout,gS};
+ `endif
+ RippleCarryAdder#(M+i) adder( .A(gA), .B(gB), .S(gS), .Cin (1'b0), .Cout(Cout) );
+end
+endgenerate
+
+`ifdef macro_args
+// Cleanup global space
+`undef calc_pp_range
+`undef calc_pp_msb
+`undef calc_pp_lsb
+`endif
+endmodule
+
+module Multiplier_2D #(parameter M = 4, parameter N = 4)(
+input [M-1:0] A, //Input A, size M
+input [N-1:0] B, //Input B, size N
+output [M+N-1:0] P ); //Output P (product), size M+N
+
+wire [M+N-1:0] PP [N-1:0];
+
+// Note: bits PP[0][M+N-1:M+1] are never used. Unused bits are optimized out during synthesis
+//assign PP[0][M:0] = { {1'b0} , { A & {M{B[0]}} } };
+//assign PP[0][M+N-1:M+1] = {(N-1){1'b0}}; // uncomment to make probing readable
+assign PP[0] = { {N{1'b0}} , { A & {M{B[0]}} } };
+assign P = PP[N-1];
+
+genvar i;
+generate
+for (i=1; i < N; i=i+1)
+begin: addPartialProduct
+ wire [M+i-1:0] gA,gB,gS; wire Cout;
+ assign gA = { A & {M{B[i]}} , {i{1'b0}} };
+ assign gB = PP[i-1][M+i-1:0];
+ //assign PP[i][M+i:0] = {Cout,gS};
+ //if (i+1<N) assign PP[i][M+N-1:M+i+1] = {(N-i){1'b0}}; // uncomment to make probing readable
+ assign PP[i] = { {(N-i){1'b0}}, Cout, gS};
+ RippleCarryAdder#(M+i) adder(
+ .A(gA), .B(gB), .S(gS), .Cin(1'b0), .Cout(Cout) );
+end
+endgenerate
+
+//always@* foreach(S[i]) $display("S[%0d]:%b",i,S[i]);
+
+endmodule
+
+module RippleCarryAdder#(parameter N = 4)(A,B,Cin,S,Cout);
+
+input [N-1:0] A;
+input [N-1:0] B;
+input Cin;
+output [N-1:0] S;
+output Cout;
+wire [N:0] CC;
+
+assign CC[0] = Cin;
+assign Cout = CC[N];
+genvar i;
+generate
+for (i=0; i < N; i=i+1)
+begin: addbit
+ FullAdder unit(A[i],B[i],CC[i],S[i],CC[i+1]);
+end
+endgenerate
+
+endmodule
+
+module FullAdder(input A,B,Cin, output wire S,Cout);
+assign {Cout,S} = A+B+Cin;
+endmodule