`timescale 1ns / 1ps
(* DONT_TOUCH = "true" *)
module HA(
    input x,y,
    output cout,s);
    assign cout = x & y;
    assign s = x ^ y;
endmodule

(* DONT_TOUCH = "true" *)
module FA(
    input x,y,ci,
    output cout,s);

wire n0,n1,n2,n3,n4;
HA ha0 (.x(x), .y(y), .cout(n0), .s(n1));
HA ha1 (.x(n1), .y(ci), .cout(n2), .s(n3));
OR or0 (.I1(n0), .I2(n2), .O(n4));
assign cout = n4;
assign s = n3; 
endmodule

module RCA(
    input [3:0] x,y,
    input ci,
    output [3:0] s,
    output cout);
wire n0,n1,n2;

FA fa0 (.x(x[0]), .y(y[0]), .ci(ci), .cout(n0), .s(s[0]));
FA fa1 (.x(x[1]), .y(y[1]), .ci(n0), .cout(n1), .s(s[1]));
FA fa2 (.x(x[2]), .y(y[2]), .ci(n1), .cout(n2), .s(s[2]));
FA fa3 (.x(x[3]), .y(y[3]), .ci(n2), .cout(cout), .s(s[3]));
endmodule



(* DONT_TOUCH = "true" *) 
module parametric_RCA #(parameter SIZE = 8) (
    input [SIZE-1:0] x,y,
    input ci,
    output [SIZE-1:0] s,
    output cout); 

wire [SIZE-1:0] c_n;
assign c_n[0] = ci;
genvar i;
generate
    for(i=0; i<SIZE; i=i+1)
    begin
        FA fax (.x(x[i]), .y(y[i]), .ci(c_n[i]), .cout(c_n[i+1]), .s(s[i]));
    end
endgenerate
assign cout = c_n[SIZE-1];
endmodule


(* DONT_TOUCH = "true" *) 
module CLA(
    input [3:0] x,y,
    input ci,
    output [3:0] s,
    output cout);
wire [3:0] g,p;
wire [4:0] c;

genvar i;
generate
for(i=0; i<4; i=i+1)
begin
    assign g[i] = x[i] & y[i];
    assign p[i] = x[i] ^ y[i];
end
endgenerate

assign c[0] = ci;
assign c[1] = g[0] | (p[0] & c[0]);
assign c[2] = g[1] | (g[0] & p[1]) | (c[0] & p[0] & p[1]);
assign c[3] = g[2] | (g[1] & p[2]) | (g[0] & p[1] & p[2]) | (c[0] & p[0] & p[1] & p[2]);
assign c[4] = g[3] | (g[2] & p[3]) | (g[1] & p[2] & p[3]) | (g[0] & p[1] & p[2] & p[3]) | (c[0] & p[0] & p[1] & p[2] & p[3]);

assign s = x ^ y ^ c[3:0];
assign cout = c[4];
endmodule

module SRCA(
    input [3:0] x,y,
    input ci,
    output [4:0] s);
wire signed [4:0] sgn_out;
RCA rca0(.x(x), .y(y) ,.ci(ci), .s(sgn_out[3:0]), .cout(sgn_out[4]));
assign s = sgn_out;
endmodule