65. Ripple Carry Adder

How do you plan to solve it?

module full_adder_1bit (
    input  a, b, cin,
    output sum, cout
);
    assign sum  = a ^ b ^ cin;
    assign cout = (a & b) | (b & cin) | (a & cin);
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
);

    // Internal carries
    wire c1, c2, c3;

    // LSB
    full_adder_1bit fa0 (a[0], b[0], cin, sum[0], c1);

    full_adder_1bit fa1 (a[1], b[1], c1, sum[1], c2);

    full_adder_1bit fa2 (a[2], b[2], c2, sum[2], c3);

    // MSB
    full_adder_1bit fa3 (a[3], b[3], c3, sum[3], cout);

endmodule