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dstar: Improve conversion from DRA to BA.

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Extended former conversion from DRA->DBA to handle
the case where some SCC is not DBA-realizable.

* src/dstarparse/dra2dba.cc: Rename as...
* src/dstarparse/dra2ba.cc: ... this.
(dra_to_dba, dra_to_dba_worker): Rename as...
(dra_to_ba, dra_to_ba_worker): ... these and extend.
* src/dstarparse/Makefile.am, src/dstarparse/public.hh,
src/dstarparse/dstar2tgba.cc, src/dstarparse/nra2nba.cc: Adjust.
* NEWS: Update the description of dstar2tgba accordingly.
This commit is contained in:
Alexandre Duret-Lutz 2013-08-17 13:10:41 +02:00
parent c58bfbd2ee
commit d7027c34d3
6 changed files with 128 additions and 38 deletions
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src/dstarparse/dra2ba.cc Normal file
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// Copyright (C) 2013 Laboratoire de Recherche et Développement 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 "public.hh"
#include "tgba/tgbamask.hh"
#include "tgbaalgos/scc.hh"
#include "tgbaalgos/reachiter.hh"
#include "tgbaalgos/gtec/gtec.hh"
#include "tgbaalgos/sccfilter.hh"
#include "ltlast/constant.hh"
namespace spot
{
// IMPORTANT NOTE: If you attempt to follow Krishnan et
// al. (ISAAC'94) paper while reading this code, make sure you
// understand the difference between their Rabin acceptance
// definition and the one we are using.
//
// Here, a cycle is accepting in a Rabin automaton if there exists
// an acceptance pair (Lᵢ, Uᵢ) such that some states from Lᵢ are
// visited while no states from Uᵢ are visited. This is the
// same definition used by ltl2dstar.
//
// In the Krishnan et al. paper, a cycle is accepting in a Rabin
// automaton if there exists an acceptance pair (Lᵢ, Uᵢ) such that
// some states from Lᵢ are visited and all visited states belongs to
// Uᵢ. In other words, you can switch from one definition to
// the other by complementing the Uᵢ set.
//
// This is a source of confusion; you have been warned.
// This function is defined in nra2nba.cc, and used only here.
SPOT_LOCAL
tgba* nra_to_nba(const dstar_aut* nra, const tgba* aut);
namespace
{
typedef std::list<const state*> state_list;
// The function that takes aut and dra is first arguments are
// either called on the main automaton, in which case dra->aut ==
// aut, or it is called on a sub-automaton in which case aut is a
// masked version of dra->aut. So we should always explore the
// automaton aut, but because the state of aut are states of
// dra->aut, we can use dra->aut to get labels, and dra->acccs to
// retrive acceptances.
static bool
filter_states(const tgba* aut,
const dstar_aut* dra,
const state_list& sl,
state_list& final,
state_list& nonfinal);
static bool
filter_scc(const tgba* aut,
const dstar_aut* dra,
state_list& final,
state_list& nonfinal)
{
// Iterate over all non-trivial SCCs.
scc_map sm(aut);
sm.build_map();
for (unsigned scc_max = sm.scc_count(), scc = 0;
scc < scc_max; ++scc)
{
if (sm.trivial(scc))
{
nonfinal.push_back(sm.one_state_of(scc));
continue;
}
// Get the list of states of that SCC
const std::list<const state*>& sl = sm.states_of(scc);
assert(!sl.empty());
if (!filter_states(aut, dra, sl, final, nonfinal))
return false;
}
return true;
}
static bool
filter_states(const tgba* aut,
const dstar_aut* dra,
const state_list& sl,
state_list& final,
state_list& nonfinal)
{
// Check whether the SCC composed of all states in sl contains
// non-accepting cycles.
//
// A cycle is accepting (in a Rabin automaton) if there exists
// an acceptance pair (Lᵢ, Uᵢ) such that some states from Lᵢ
// are visited while no states from Uᵢ are visited.
//
// Consequently, a cycle is non-accepting if for all acceptance
// pairs (Lᵢ, Uᵢ), either no states from Lᵢ are visited or some
// states from Uᵢ are visited. (This corresponds to an
// accepting cycle with Streett acceptance.)
//
// Now we consider the SCC as one large cycle and check its
// intersection with all Lᵢs and Uᵢs. Let l=[l₁,l₂,...] and
// u=[u₁,u₂,...] be bitvectors where bit lᵢ (resp. uᵢ)
// indicates that Lᵢ (resp. Uᵢ) has been visited in the SCC.
state_list::const_iterator it = sl.begin();
int num = dra->aut->get_label(*it++);
bitvect* l = dra->accsets->at(num * 2).clone();
bitvect* u = dra->accsets->at(num * 2 + 1).clone();
for (; it != sl.end(); ++it)
{
num = dra->aut->get_label(*it);
*l |= dra->accsets->at(num * 2);
*u |= dra->accsets->at(num * 2 + 1);
}
// If we have l&!u = [0,0,...] that means that the cycle formed
// by the entire SCC is not accepting. However that does not
// necessarily imply that all cycles in the SCC are also
// non-accepting. We may have a smaller cycle that is
// accepting, but which becomes non-accepting when extended with
// more states.
*l -= *u;
delete u;
if (l->is_fully_clear())
{
delete l;
// Check whether the SCC is accepting. We do that by simply
// converting that SCC into a TGBA and running our emptiness
// check. This is not a really smart implementation and
// could be improved.
{
state_set keep(sl.begin(), sl.end());
const tgba* masked =
build_tgba_mask_keep(dra->aut, keep, sl.front());
const tgba* nba = nra_to_nba(dra, masked);
emptiness_check* ec = couvreur99(nba);
emptiness_check_result* ecr = ec->check();
delete ecr;
delete ec;
delete nba;
delete masked;
if (ecr)
{
// This SCC is not DBA-realizable.
//std::cerr << "not DBA-realizable\n";
return false;
}
}
//std::cerr << "non-accepting\n";
for (state_list::const_iterator i = sl.begin();
i != sl.end(); ++i)
nonfinal.push_back(*i);
return true;
}
// The bits sets in *l corresponds to Lᵢs that have been seen
// without seeing the matching Uᵢ. In this SCC, any state in Lᵢ
// is therefore final. Otherwise we do not know: it is possible
// that there is a non-accepting cycle in the SCC that do not
// visit Lᵢ.
state_set unknown;
for (it = sl.begin(); it != sl.end(); ++it)
{
num = dra->aut->get_label(*it);
bitvect* l2 = dra->accsets->at(num * 2).clone();
*l2 &= *l;
if (!l2->is_fully_clear())
{
final.push_back(*it);
}
else
{
unknown.insert(*it);
}
delete l2;
}
delete l;
// Check whether it is possible to build non-accepting cycles
// using only the "unknown" states.
while (!unknown.empty())
{
//std::cerr << "unknown\n";
// Build a sub-automaton for just the unknown states,
// starting from any state in the SCC.
const tgba* scc_mask =
build_tgba_mask_keep(aut, unknown, *unknown.begin());
state_list local_final;
state_list local_nonfinal;
bool dbarealizable =
filter_scc(scc_mask, dra, local_final, local_nonfinal);
delete scc_mask;
if (!dbarealizable)
return false;
for (state_list::const_iterator i = local_final.begin();
i != local_final.end(); ++i)
unknown.erase(*i);
final.splice(final.end(), local_final);
for (state_list::const_iterator i = local_nonfinal.begin();
i != local_nonfinal.end(); ++i)
unknown.erase(*i);
nonfinal.splice(nonfinal.end(), local_nonfinal);
}
return true;
}
class dra_to_ba_worker: public tgba_reachable_iterator_depth_first
{
public:
dra_to_ba_worker(const dstar_aut* a,
const state_set& final,
const scc_map& sm,
const std::vector<bool>& realizable):
tgba_reachable_iterator_depth_first(a->aut),
in_(a),
out_(new tgba_explicit_number(a->aut->get_dict())),
final_(final),
num_states_(a->aut->num_states()),
sm_(sm),
realizable_(realizable)
{
bdd_dict* bd = a->aut->get_dict();
bd->register_all_variables_of(a->aut, out_);
// Invent a new acceptance set for the degeneralized automaton.
int accvar =
bd->register_acceptance_variable(ltl::constant::true_instance(),
out_);
acc_ = bdd_ithvar(accvar);
out_->set_acceptance_conditions(acc_);
}
tgba_explicit_number*
result()
{
return out_;
}
void
process_link(const state* sin, int,
const state* sout, int,
const tgba_succ_iterator* si)
{
int in = in_->aut->get_label(sin);
int out = in_->aut->get_label(sout);
unsigned in_scc = sm_.scc_of_state(sin);
typedef state_explicit_number::transition trans;
trans* t = out_->create_transition(in, out);
bdd cond = t->condition = si->current_condition();
if (realizable_[in_scc])
{
if (final_.find(sin) != final_.end())
t->acceptance_conditions = acc_;
}
else if (sm_.scc_of_state(sout) == in_scc)
{
// Create one clone of the SCC per accepting pair,
// removing states from the Ui part of the (Li, Ui) pairs.
// (Or the Ei part of Löding's (Ei, Fi) pairs.)
bitvect& l = in_->accsets->at(2 * in);
bitvect& u = in_->accsets->at(2 * in + 1);
for (size_t i = 0; i < in_->accpair_count; ++i)
{
int shift = num_states_ * (i + 1);
// In the Ui set. (Löding's Ei set.)
if (!u.get(i))
{
// Transition t1 is a non-deterministic jump
// from the original automaton to the i-th clone.
//
// Transition t2 constructs the clone.
//
// Löding creates transition t1 regardless of the
// acceptance set. We restrict it to the non-Li
// states. Both his definition and this
// implementation create more transitions than needed:
// we do not need more than one transition per
// accepting cycle.
trans* t1 = out_->create_transition(in, out + shift);
t1->condition = cond;
trans* t2 = out_->create_transition(in + shift,
out + shift);
t2->condition = cond;
// In the Li set. (Löding's Fi set.)
if (l.get(i))
t2->acceptance_conditions = acc_;
}
}
}
}
protected:
const dstar_aut* in_;
tgba_explicit_number* out_;
const state_set& final_;
size_t num_states_;
bdd acc_;
const scc_map& sm_;
const std::vector<bool>& realizable_;
};
}
tgba* dra_to_ba(const dstar_aut* dra, bool* dba)
{
assert(dra->type == Rabin);
state_list final;
state_list nonfinal;
// Iterate over all non-trivial SCCs.
scc_map sm(dra->aut);
sm.build_map();
unsigned scc_max = sm.scc_count();
bool dba_realizable = true;
std::vector<bool> realizable(scc_max);
for (unsigned scc = 0; scc < scc_max; ++scc)
{
if (sm.trivial(scc))
{
realizable[scc] = true;
continue;
}
// Get the list of states of that SCC
const std::list<const state*>& sl = sm.states_of(scc);
assert(!sl.empty());
bool scc_realizable = filter_states(dra->aut, dra, sl, final, nonfinal);
dba_realizable &= scc_realizable;
realizable[scc] = scc_realizable;
//std::cerr << "realizable[" << scc << "] = " << scc_realizable << "\n";
}
if (dba)
*dba = dba_realizable;
// for (state_list::const_iterator i = final.begin();
// i != final.end(); ++i)
// std::cerr << dra->aut->get_label(*i) << " is final\n";
// for (state_list::const_iterator i = nonfinal.begin();
// i != nonfinal.end(); ++i)
// std::cerr << dra->aut->get_label(*i) << " is non-final\n";
state_set fs(final.begin(), final.end());
dra_to_ba_worker w(dra, fs, sm, realizable);
w.run();
tgba_explicit_number* res1 = w.result();
tgba* res2 = scc_filter_states(res1);
delete res1;
return res2;
}
}