spot/src/tgbaalgos/isweakscc.cc

// -*- coding: utf-8 -*-
// Copyright (C) 2012, 2013, 2014 Laboratoire de Recherche et
// Developpement de l'Epita (LRDE).
//
// 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 "cycles.hh"
#include "ltlast/formula.hh"
#include "isweakscc.hh"

namespace spot
{
  namespace
  {
    // Look for a non-accepting cycle.
    class weak_checker: public enumerate_cycles
    {
    public:
      bool result;

      weak_checker(const scc_map& map)
	: enumerate_cycles(map), result(true)
      {
      }

      virtual bool
      cycle_found(const state* start)
      {
	dfs_stack::const_reverse_iterator i = dfs_.rbegin();
	bdd acc = bddfalse;
	for (;;)
	  {
	    acc |= i->succ->current_acceptance_conditions();
	    if (i->ts->first == start)
	      break;
	    ++i;
	    // The const cast is here to please old g++ versions.
	    // At least version 4.0 needs it.
	    assert(i != const_cast<const dfs_stack&>(dfs_).rend());
	  }
	if (acc != aut_->all_acceptance_conditions())
	  {
	    // We have found an non-accepting cycle, so the SCC is not
	    // weak.
	    result = false;
	    return false;
	  }
	return true;
      }

    };
  }

  bool
  is_inherently_weak_scc(scc_map& map, unsigned scc)
  {
    // If no cycle is accepting, the SCC is weak.
    if (!map.accepting(scc))
      return true;
    // If the SCC is accepting, but one cycle is not, the SCC is not
    // weak.
    weak_checker w(map);
    w.run(scc);
    return w.result;
  }

  bool
  is_weak_scc(scc_map& map, unsigned scc)
  {
    // If no cycle is accepting, the SCC is weak.
    if (!map.accepting(scc))
      return true;
    // If all transitions use all acceptance conditions, the SCC is weak.
    return (map.useful_acc_of(scc)
	    == bdd_support(map.get_aut()->neg_acceptance_conditions()));
  }

  bool
  is_complete_scc(scc_map& map, unsigned scc)
  {
    auto a = map.get_aut();
    for (auto s: map.states_of(scc))
      {
	tgba_succ_iterator* it = a->succ_iter(s);

	// If a state has no successors, the SCC is not complete.
	if (!it->first())
	  {
	    a->release_iter(it);
	    return false;
	  }

	// Sum guards on all outgoing transitions.
	bdd sumall = bddfalse;
	do
	  {
	    const state *next = it->current_state();
	    // check it's the same scc
	    if (map.scc_of_state(next) == scc)
	      sumall |= it->current_condition();
	    next->destroy();
	    if (sumall == bddtrue)
	      break;
	  }
	while (it->next());
	a->release_iter(it);

	if (sumall != bddtrue)
	  return false;
      }
    return true;
  }

  bool
  is_terminal_scc(scc_map& map, unsigned scc)
  {
    // If all transitions use all acceptance conditions, the SCC is weak.
    return ((map.useful_acc_of(scc) ==
	     bdd_support(map.get_aut()->neg_acceptance_conditions()))
	    && is_complete_scc(map, scc));
  }
}