GOF can automatically generate complicated gate symbol from
the logic function.
For example: ADD/SUB gate
module it15_bmux1_0 (ZN,ADD,DI,SUB);
output ZN;
input ADD;
input DI;
input SUB;
not u0 (t0,DI);
and u1 (t1,ADD,t0);
or u2 (t2,ADD,DI);
and u3 (t3,SUB,t2);
or u4 (ZN,t1,t3);
endmodule
