X-FULL ADDER:- (4i/p-1bitwide adder)

module xfa (cout2,cout1,s,a,b,c,d); 
input a,b,c,d;
output cout2,cout1,s;
wire c1,s1,c2;
fa f1 (c1,s1,a,b,c);
ha h1 (c2,s,s1,d);
ha h2 (cout2,cout1,c1,c2);
endmodule

 TEST BENCH:-

module adtb ();

reg a,b,c,d;
wire cout2,cout1,s;
xfa dut (cout2,cout1,s,a,b,c,d); 
integer j;
initial
begin
for (j=0;j<=15;j=j+1)
begin
{a,b,c,d}= j;
#1;
$display(a,b,c,d,":",cout2,cout1,s);
end
end
endmodule