bool Atpg::Backtrace() {
Gate *g = &cir_->gates_[current_obj_.first];
Value objv = current_obj_.second;
while (!(g->type_==Gate::PI
|| g->type_==Gate::PPI)) { // while objective net not fed by P/PI
if (g->getOutputCtrlValue()==X) { //NOT, BUF, TODO: XOR, XNOR
if (g->type_==Gate::INV)
objv = EvalNot(objv);
g = &cir_->gates_[g->fis_[0]];
assert(impl_->GetVal(g->id_)==X);
continue;
}
Gate *gnext = NULL;
if (objv==EvalNot(g->getOutputCtrlValue())) { // if objv is easy to set
// choose input of "g" which
// 1) is at X
// 2) is easiest to control
gnext = FindEasiestToSetFanIn(g, objv);
}
else if (objv==g->getOutputCtrlValue()) { // is objv is hard to set
// choose input of "g" which
// 1) is at X
// 2) is hardest to control
gnext = FindHardestToSetFanIn(g, objv);
}
if (g->isInverse())
objv = EvalNot(objv);
g = gnext;
}
return impl_->MakeDecision(g, objv);
}
