65. Ripple Carry Adder

How do you plan to solve it?

// 1-bit Full Adder (to be used by the 4-bit RCA)
module full_adder_1bit (
    input  a, b, cin,
    output sum, cout
);
    wire [2:0] w;
    assign w[0] = a ^ b;
    assign w[1] = a & b;
    assign sum = w[0] ^ cin;
    assign w[2] = w[0] & cin;
    assign cout = w[2] | w[1];
endmodule



// 4-bit Ripple Carry Adder – chain 4 full adders
module rca4_chain (
    input  [3:0] a,
    input  [3:0] b,
    input        cin,
    output [3:0] sum,
    output       cout
);
    wire [3:0] w;
    full_adder_1bit full0(.a(a[0]),.b(b[0]),.cin(cin),.sum(sum[0]),.cout(w[0]));
    full_adder_1bit full1(.a(a[1]),.b(b[1]),.cin(w[0]),.sum(sum[1]),.cout(w[1]));
    full_adder_1bit full2(.a(a[2]),.b(b[2]),.cin(w[1]),.sum(sum[2]),.cout(w[2]));
    full_adder_1bit full3(.a(a[3]),.b(b[3]),.cin(w[2]),.sum(sum[3]),.cout(cout));

endmodule