Arithmetic circuits- Full subtractor using gates

FULL SUBTRACTOR GATE LEVEL MODEL

module fsvj(borrow,diff,a,b,c);
output borrow,diff;
input a,b,c;
wire w1,w2,w3,w4,w5,w6,w7;
xor (diff,a,b,c);
not n1(w1,a);
not n2(w2,b);
not n3(w3,c);
and a1(w4,a,b,c);
and a2(w5,w1,b,c);
and a3(w6,w1,w2,c);
and a4(w7,w1,b,c);
or o1(borrow,w4,w5,w6,w7);
endmodule