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module fulladder1(sum, co, a, b, c_in);
output sum, co;
input a, b, c_in;
always @(a, b, c_in)
$display("fa1: a=%b, b=%b, c_in=%b", a, b, c_in);
assign sum = a ^ b ^ c_in;
assign co = (a & b) | (b & c_in) | (c_in & a);
endmodule
module fulladder2(sum, cout, a, b, cin);
output [1:0] sum;
output cout;
input [1:0] a, b;
input cin;
wire c;
always @(a, b, cin)
$display("fa2: a=%b, b=%b, cin=%b", a, b, cin);
// Instantiate four 1-bit full adders
fulladder1 f0 (sum[0], c, a[0], b[0], cin);
fulladder1 f2 (sum[1], cout, a[1], b[1], c);
endmodule
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