complete.cc

// -*- coding: utf-8 -*-
// Copyright (C) 2013, 2014 Laboratoire de Recherche et Développement
// de l'Epita.
//
// This file is part of Spot, a model checking library.
//
// Spot is free software; you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
//
// Spot is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
// License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

#include "complete.hh"
#include "dupexp.hh"

namespace spot
{
  unsigned tgba_complete_here(tgba_digraph* aut)
  {
    unsigned n = aut->num_states();
    unsigned sink = -1U;
    bdd allacc = aut->all_acceptance_conditions();
    if (allacc == bddfalse)
      {
	// We cannot safely complete an automaton if it has no
	// acceptance set as the added sink would become accepting.
	// In this case, add an acceptance set to all transitions.
	allacc = aut->set_single_acceptance_set();
	for (auto& t: aut->transitions())
	  t.acc = allacc;
      }
    else
      {
	// If some acceptance sets were used, loop over the states and
	// seek a state that has only self loops, and that is not
	// accepting.  This will be our sink state.
	for (unsigned i = 0; i < n; ++i)
	  {
	    bool selfloop = true;
	    bdd accsum = bddfalse;
	    for (auto& t: aut->out(i))
	      {
		if (t.dst != i)	// Not a self-loop
		  {
		    selfloop = false;
		    break;
		  }
		accsum |= t.acc;
	      }
	    if (selfloop && accsum != allacc) // We have found a sink!
	      {
		sink = i;
		break;
	      }
	  }
      }
    // If we haven't found any sink, simply add one.
    if (sink == -1U)
      {
	sink = aut->new_state();
	++n;
      }

    // Now complete all states (including the sink).
    for (unsigned i = 0; i < n; ++i)
      {
	bdd missingcond = bddtrue;
	bdd acc = bddfalse;
	for (auto& t: aut->out(i))
	  {
	    missingcond -= t.cond;
	    // FIXME: This is ugly.
	    //
	    // In case the automaton uses state-based acceptance, we
	    // need to put the new transition in the same set as all
	    // the other.
	    //
	    // In case the automaton uses transition-based acceptance,
	    // it does not matter what acceptance set we put the new
	    // transition into.
	    //
	    // So in both cases, we put the transition in the same
	    // acceptance sets as the last outgoing transition of the
	    // state.
	    acc = t.acc;
	  }
	// In case the automaton use state-based acceptance, propagate
	// the acceptance of the first transition to the one we add.
	if (missingcond != bddfalse)
	  aut->new_transition(i, sink, missingcond, acc);
      }
    return sink;
  }

  tgba_digraph* tgba_complete(const tgba* aut)
  {
    tgba_digraph* res = tgba_dupexp_dfs(aut);
    tgba_complete_here(res);
    return res;
  }

}