sccfilter.cc 9.99 KB
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// -*- coding: utf-8 -*-
// Copyright (C) 2009, 2010, 2011, 2012, 2013 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 "sccfilter.hh"
#include "tgba/tgbaexplicit.hh"
#include "reachiter.hh"
#include "tgbaalgos/scc.hh"

namespace spot
{
  namespace
  {
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    // BDD.id -> Acc number
    typedef std::map<int, unsigned> accremap_t;
    typedef std::vector<accremap_t> remap_table_t;

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    static
    state_explicit_number::transition*
    create_transition(const tgba*, tgba_explicit_number* out_aut,
		      const state*, int in, const state*, int out)
    {
      return out_aut->create_transition(in, out);
    }

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    static
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    state_explicit_string::transition*
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    create_transition(const tgba* aut, tgba_explicit_string* out_aut,
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		      const state* in_s, int, const state* out_s, int)
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    {
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      const tgba_explicit_string* a =
	static_cast<const tgba_explicit_string*>(aut);
      return out_aut->create_transition(a->get_label(in_s),
					a->get_label(out_s));
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    }

    static
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    state_explicit_formula::transition*
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    create_transition(const tgba* aut, tgba_explicit_formula* out_aut,
		      const state* in_s, int, const state* out_s, int)
    {
      const tgba_explicit_formula* a =
	static_cast<const tgba_explicit_formula*>(aut);
      const ltl::formula* in_f = a->get_label(in_s);
      const ltl::formula* out_f = a->get_label(out_s);
      if (!out_aut->has_state(in_f))
	in_f->clone();
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      if ((in_f != out_f) && !out_aut->has_state(out_f))
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	out_f->clone();
      return out_aut->create_transition(in_f, out_f);
    }

    template<class T>
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    class filter_iter: public tgba_reachable_iterator_depth_first
    {
    public:
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      typedef T output_t;
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      typedef std::map<int, bdd> map_t;
      typedef std::vector<map_t> remap_t;
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      filter_iter(const tgba* a,
		  const scc_map& sm,
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		  const std::vector<bool>& useless,
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		  remap_table_t& remap_table,
		  unsigned max_num,
		  const std::vector<unsigned>& max_table,
		  bool remove_all_useless)
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	: tgba_reachable_iterator_depth_first(a),
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	  out_(new T(a->get_dict())),
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	  sm_(sm),
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	  useless_(useless),
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	  max_num_(max_num),
	  all_(remove_all_useless),
	  acc_(max_num)
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      {
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	acc_[0] = bddfalse;
	bdd tmp = a->all_acceptance_conditions();
	bdd_dict* d = a->get_dict();
	assert(a->number_of_acceptance_conditions() >= max_num_ - 1);
	if (tmp != bddfalse)
	  {
	    for (unsigned n = max_num_ - 1; n > 0; --n)
	      {
		assert(tmp != bddfalse);
		const ltl::formula* a = d->oneacc_to_formula(bdd_var(tmp));
		out_->declare_acceptance_condition(a->clone());
		tmp = bdd_low(tmp);
	      }
	    tmp = a->all_acceptance_conditions();
	    for (unsigned n = max_num_ - 1; n > 0; --n)
	      {
		const ltl::formula* a = d->oneacc_to_formula(bdd_var(tmp));
		acc_[n] = out_->get_acceptance_condition(a->clone());
		tmp = bdd_low(tmp);
	      }
	  }
	else
	  {
	    assert(max_num_ == 1);
	  }

	unsigned c = sm.scc_count();
	remap_.resize(c);
	bdd all_orig_neg = aut_->neg_acceptance_conditions();
	bdd all_sup = bdd_support(all_orig_neg);

	for (unsigned n = 0; n < c; ++n)
	  {
	    if (!sm.accepting(n))
	      continue;

	    bdd missingacc = bddfalse;
	    for (unsigned a = max_table[n]; a < max_num_; ++a)
	      missingacc |= acc_[a];

	    bdd all = sm.useful_acc_of(n);
	    while (all != bddfalse)
	      {
		bdd one = bdd_satoneset(all, all_sup, bddtrue);
		all -= one;
		bdd res = bddfalse;
		bdd resacc = bddfalse;
		while (one != bddtrue)
		  {
		    if (bdd_high(one) == bddfalse)
		      {
			one = bdd_low(one);
			continue;
		      }
		    int vn = bdd_var(one);
		    bdd v = bdd_ithvar(vn);
		    resacc |= bdd_exist(all_orig_neg, v) & v;
		    res |= acc_[remap_table[n][vn]];
		    one = bdd_high(one);
		  }
		if (res != bddfalse)
		  res |= missingacc;
		int id = resacc.id();
		remap_[n][id] = res;
	      }
	  }
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      }

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      T*
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      result()
      {
	return out_;
      }

      bool
      want_state(const state* s) const
      {
	return !useless_[sm_.scc_of_state(s)];
      }

      void
      process_link(const state* in_s, int in,
		   const state* out_s, int out,
		   const tgba_succ_iterator* si)
      {
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	typename output_t::state::transition* t =
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	  create_transition(this->aut_, out_, in_s, in, out_s, out);
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	out_->add_conditions(t, si->current_condition());

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	// Regardless of all_, do not output any acceptance condition
	// if the destination is not in an accepting SCC.
	//
	// If all_ is set, do not output any acceptance condition if the
	// source is not in the same SCC as dest.
	//
	// (See the documentation of scc_filter() for a rational.)
	unsigned u = sm_.scc_of_state(out_s);
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	unsigned v = sm_.scc_of_state(in_s);
	if (sm_.accepting(u) && (!all_ || u == v))
	  {
	    bdd acc = si->current_acceptance_conditions();
	    if (acc == bddfalse)
	      return;
	    t->acceptance_conditions = remap_[u][acc.id()];
	  }
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      }

    private:
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      T* out_;
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      const scc_map& sm_;
      const std::vector<bool>& useless_;
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      unsigned max_num_;
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      bool all_;
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      std::vector<bdd> acc_;
      remap_t remap_;
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    };
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  } // anonymous


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  tgba* scc_filter(const tgba* aut, bool remove_all_useless)
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  {
    scc_map sm(aut);
    sm.build_map();
    scc_stats ss = build_scc_stats(sm);

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    remap_table_t remap_table(ss.scc_total);
    std::vector<unsigned> max_table(ss.scc_total);
    unsigned max_num = 1;

    for (unsigned n = 0; n < ss.scc_total; ++n)
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      {
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	if (!sm.accepting(n))
	  continue;
	bdd all = sm.useful_acc_of(n);
	bdd negall = aut->neg_acceptance_conditions();
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	// Compute a set of useless acceptance conditions.
	// If the acceptance combinations occurring in
	// the automata are  { a, ab, abc, bd }, then
	// ALL contains (a&!b&!c&!d)|(a&b&!c&!d)|(a&b&c&!d)|(!a&b&!c&d)
	// and we want to find that 'a' and 'b' are useless because
	// they always occur with 'c'.
	// The way we check if 'a' is useless is to look whether ALL
	// implies (x -> a) for some other acceptance condition x.
	bdd allconds = bdd_support(negall);
	bdd allcondscopy = allconds;
	bdd useless = bddtrue;
	while (allconds != bddtrue)
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	  {
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	    // Speed-up the computation of implied acceptance by
	    // removing those that are always present.  We detect
	    // those that appear as conjunction of positive variables
	    // at the start of ALL.
	    bdd prefix = bdd_satprefix(all);
	    if (prefix != bddtrue)
	      {
		assert(prefix == bdd_support(prefix));
		allcondscopy = bdd_exist(allcondscopy, prefix);
		if (allcondscopy != bddtrue)
		  {
		    useless &= prefix;
		  }
		else
		  {
		    // Never erase all conditions: at least keep one.
		    useless &= bdd_high(prefix);
		    break;
		  }
		allconds = bdd_exist(allconds, prefix);
	      }

	    // Pick a non-useless acceptance condition a.
	    bdd a = bdd_ithvar(bdd_var(allconds));
	    // For all acceptance condition x that is not already useless...
	    bdd others = allcondscopy;
	    while (others != bddtrue)
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	      {
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		bdd x = bdd_ithvar(bdd_var(others));
		// ... check whether it always implies a.
		if (x != a && bdd_implies(all, x >> a))
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		  {
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		    // If so, a is useless.
		    all = bdd_exist(all, a);
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		    useless &= a;
		    allcondscopy = bdd_exist(allcondscopy, a);
		    break;
		  }
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		others = bdd_high(others);
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	      }
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	    allconds = bdd_high(allconds);
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	  }

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	// We never remove ALL acceptance marks.
	assert(negall == bddtrue || useless != bdd_support(negall));
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	bdd useful = bdd_exist(negall, useless);

	// Go over all useful sets of acceptance marks, and give them
	// a number.
	unsigned num = 1;
	// First compute the number of acceptance conditions used.
	for (BDD c = useful.id(); c != 1; c = bdd_low(c))
	  ++num;
	max_table[n] = num;
	if (num > max_num)
	  max_num = num;
	// Then number all of these acceptance conditions in the
	// reverse order.  This makes sure that the associated number
	// varies in the same direction as the bdd variables, which in
	// turn makes sure we preserve the acceptance condition
	// ordering (which matters for degeneralization).
	for (BDD c = useful.id(); c != 1; c = bdd_low(c))
	  remap_table[n].insert(std::make_pair(bdd_var(c), --num));
      }
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    // In most cases we will create a tgba_explicit_string copy of the
    // initial tgba, but this is not very space efficient as the
    // labels are built using the "format_state()" string output of
    // the original automaton.  In the case where the source automaton is
    // a tgba_explicit_formula (typically after calling ltl2tgba_fm())
    // we can create another tgba_explicit_formula instead.
    const tgba_explicit_formula* af =
      dynamic_cast<const tgba_explicit_formula*>(aut);
    if (af)
      {
	filter_iter<tgba_explicit_formula> fi(af, sm, ss.useless_scc_map,
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					      remap_table, max_num,
					      max_table, remove_all_useless);
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	fi.run();
	tgba_explicit_formula* res = fi.result();
	res->merge_transitions();
	return res;
      }
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    const tgba_explicit_string* as =
      dynamic_cast<const tgba_explicit_string*>(aut);
    if (as)
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      {
	filter_iter<tgba_explicit_string> fi(aut, sm, ss.useless_scc_map,
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					     remap_table, max_num,
					     max_table, remove_all_useless);
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	fi.run();
	tgba_explicit_string* res = fi.result();
	res->merge_transitions();
	return res;
      }
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    else
      {
	filter_iter<tgba_explicit_number> fi(aut, sm, ss.useless_scc_map,
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					     remap_table, max_num,
					     max_table, remove_all_useless);
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	fi.run();
	tgba_explicit_number* res = fi.result();
	res->merge_transitions();
	return res;
      }
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  }

}