strength.cc 6.46 KB
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// -*- coding: utf-8 -*-
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// Copyright (C) 2010, 2011, 2013, 2014, 2015 Laboratoire de Recherche
// et Développement de l'Epita (LRDE)
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//
// 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
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// the Free Software Foundation; either version 3 of the License, or
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// (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
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// along with this program.  If not, see <http://www.gnu.org/licenses/>.
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#include <spot/twaalgos/strength.hh>
#include <spot/misc/hash.hh>
#include <spot/twaalgos/isweakscc.hh>
#include <spot/twaalgos/mask.hh>
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#include <deque>
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namespace spot
{
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  namespace
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  {
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    template <bool terminal, bool inweak = false, bool set = false>
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    bool is_type_automaton(const twa_graph_ptr& aut, scc_info* si)
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    {
      // Create an scc_info if the user did not give one to us.
      bool need_si = !si;
      if (need_si)
	si = new scc_info(aut);
      si->determine_unknown_acceptance();
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      bool is_inweak = true;
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      bool is_weak = true;
      bool is_term = true;
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      unsigned n = si->scc_count();
      for (unsigned i = 0; i < n; ++i)
	{
	  if (si->is_trivial(i))
	    continue;
	  bool first = true;
	  acc_cond::mark_t m = 0U;
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	  if (is_weak)
	    for (auto src: si->states_of(i))
	      for (auto& t: aut->out(src))
		if (si->scc_of(t.dst) == i)
		  {
		    if (first)
		      {
			first = false;
			m = t.acc;
		      }
		    else if (m != t.acc)
		      {
			is_weak = false;
			if (!inweak)
			  goto exit;
		      }
		  }
	  if (!is_weak && si->is_accepting_scc(i))
	    {
	      assert(inweak);
	      if (scc_has_rejecting_cycle(*si, i))
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		{
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		  is_inweak = false;
		  break;
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		}
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	    }
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	  if (terminal && si->is_accepting_scc(i) && !is_complete_scc(*si, i))
	    {
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	      is_term = false;
	      if (!set)
		break;
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	    }
	}
    exit:
      if (need_si)
	delete si;
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      if (set)
	{
	  if (terminal)
	    aut->prop_terminal(is_term && is_weak);
	  aut->prop_weak(is_weak);
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	  aut->prop_inherently_weak(is_inweak);
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	}
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      if (inweak)
	return is_inweak;
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      return is_weak && is_term;
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    }
  }
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  bool
  is_terminal_automaton(const const_twa_graph_ptr& aut, scc_info* si)
  {
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    return (aut->prop_terminal() ||
	    is_type_automaton<true>(std::const_pointer_cast<twa_graph>(aut),
				    si));
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  }
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  bool
  is_weak_automaton(const const_twa_graph_ptr& aut, scc_info* si)
  {
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    return (aut->prop_weak() ||
	    is_type_automaton<false>(std::const_pointer_cast<twa_graph>(aut),
				     si));
  }

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  bool
  is_inherently_weak_automaton(const const_twa_graph_ptr& aut, scc_info* si)
  {
    return (aut->prop_inherently_weak() ||
	    is_type_automaton<false, true>
	    (std::const_pointer_cast<twa_graph>(aut), si));
  }

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  void check_strength(const twa_graph_ptr& aut, scc_info* si)
  {
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    is_type_automaton<true, true, true>(aut, si);
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  }

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  bool is_safety_mwdba(const const_twa_graph_ptr& aut)
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  {
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    if (!(aut->acc().is_buchi() || aut->acc().is_tt()))
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      throw std::runtime_error
	("is_safety_mwdba() should be called on a Buchi automaton");

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    for (auto& t: aut->edges())
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      if (!aut->acc().accepting(t.acc))
	return false;
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    return true;
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  }
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  twa_graph_ptr
  decompose_strength(const const_twa_graph_ptr& aut, const char* keep_opt)
  {
    if (keep_opt == nullptr || *keep_opt == 0)
      throw std::runtime_error
	(std::string("option for decompose_strength() should not be empty"));

    enum strength {
      Ignore = 0,
      Terminal = 1,
      WeakStrict = 2,
      Weak = Terminal | WeakStrict,
      Strong = 4,
      Needed = 8,		// Needed SCCs are those that lead to
				// the SCCs we want to keep.
    };
    unsigned char keep = Ignore;
    while (auto c = *keep_opt++)
      switch (c)
	{
	case 's':
	  keep |= Strong;
	  break;
	case 't':
	  keep |= Terminal;
	  break;
	case 'w':
	  keep |= WeakStrict;
	  break;
	default:
	  throw std::runtime_error
	    (std::string("unknown option for decompose_strength(): ") + c);
	}

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    auto p = aut->acc().unsat_mark();
    bool all_accepting = !p.first;
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    acc_cond::mark_t wacc = 0U;	// Acceptance for weak SCCs
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    acc_cond::mark_t uacc = p.second; // Acceptance for "needed" SCCs, that
                                      // we only want to traverse.
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    // If the acceptance condition is always satisfiable, we will
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    // consider the automaton as weak (even if that is not the
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    // case syntactically) and not output any strong part.
    if (all_accepting)
      {
	keep &= ~Strong;
	if (keep == Ignore)
	  return nullptr;
      }

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    scc_info si(aut);
    si.determine_unknown_acceptance();

    unsigned n = si.scc_count();
    std::vector<unsigned char> want(n, Ignore);
    bool nonempty = false;
    bool strong_seen = false;

    for (unsigned i = 0; i < n; ++i) // SCC are topologically ordered
      {
	if (si.is_accepting_scc(i))
	  {
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	    if (all_accepting | is_weak_scc(si, i))
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	      {
		if (keep & Weak)
		  {
		    if ((keep & Weak) == Weak)
		      want[i] = Weak;
		    else
		      want[i] = keep &
			(is_complete_scc(si, i) ? Terminal : WeakStrict);
		  }
	      }
	    else
	      {
		want[i] = keep & Strong;
		strong_seen = true;
	      }
	    nonempty |= want[i];
	  }
	// An SCC is needed if one of its successor is.
	for (unsigned j: si.succ(i))
	  if (want[j])
	    {
	      want[i] |= Needed;
	      break;
	    }
      }

    if (!nonempty)
      return nullptr;

    twa_graph_ptr res = make_twa_graph(aut->get_dict());
    res->copy_ap_of(aut);
    res->prop_copy(aut, { true, false, true, false });
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    if (keep & Strong)
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      res->copy_acceptance_of(aut);
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    else
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      wacc = res->set_buchi();
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    auto fun = [&si, &want, uacc, wacc, keep]
      (unsigned src, bdd& cond, acc_cond::mark_t& acc, unsigned dst)
      {
	if (want[si.scc_of(dst)] == Ignore)
	  {
	    cond = bddfalse;
	    return;
	  }
	if (want[si.scc_of(src)] == Needed)
	  {
	    acc = uacc;
	    return;
	  }
	if (keep & Strong)
	  return;
	acc = wacc;
      };

    transform_accessible(aut, res, fun);

    if (!(keep & Strong))
      {
	res->prop_weak(true);
	if (!(keep & WeakStrict))
	  {
	    assert(keep & Terminal);
	    res->prop_terminal(true);
	  }
      }
    else
      {
	res->prop_weak(!strong_seen);
      }
    return res;
  }
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}