R2R simulation

r2r.v

`timescale 1ns / 1ps

module sig_mag_cell(
    input  [3:0] in,
    output [3:0] out,
    input  sign,
    input  cin,
    output cout
);

assign out = sign ? ~in + cin: in + cin;
assign cout = out == 4'b0000 & cin;
endmodule

module sign_mag16(
    input  [15:0] in,
    output [15:0] out,
    input  sign,
    output cout
);
wire [3:0] in0 = in[3:0];
wire [3:0] in1 = in[7:4];
wire [3:0] in2 = in[11:8];
wire [3:0] in3 = in[15:12];
wire [3:0] out0;
wire [3:0] out1;
wire [3:0] out2;
wire [3:0] out3;
wire cout0;
wire cout1;
wire cout2;
wire cout3;
wire cin = 1;
sig_mag_cell cell0(in0, out0, sign, cin, cout0);
sig_mag_cell cell1(in1, out1, sign, cout0, cout1);
sig_mag_cell cell2(in2, out2, sign, cout1, cout2);
sig_mag_cell cell3(in3, out3, sign, cout2, cout3);
assign out = {out3, out2, out1, out0};
assign cout = cout3;
endmodule

module sign_mag_router(
    input  [15:0] in,
    output [14:0] out_pos,
    output [14:0] out_neg,
    input  sign
);

assign out_pos = sign ? 15'b0 : in[14:0];
assign out_neg = sign ? in[14:0] : 15'b0;

endmodule

module r2r;
    reg  [15:0] din;
    reg  sgn;
    wire [15:0] dout;
    wire cout;
    integer i;

    wire [14:0] out_pos;
    wire [14:0] out_neg;

    sign_mag16 sign_mag (din, dout, sgn, cout);
    wire [14:0] magnitude = dout[14:0];
    sign_mag_router router (dout, out_pos, out_neg, sgn);

    initial begin
        for (i = -32768; i < 32768 ; i = i + 1) begin
            din = i & 16'h7fff;
            sgn = (i >> 15) & 1;
            #4; 
            $display("Set0 Input: %b, Sign: %b, Output: %b, Carry Out: %b, Out Pos: %b, Out Neg: %b", din, sgn, dout, cout, out_pos, out_neg);  
        end
    end
endmodule