Commit ef1bbfc6 authored by Alexandre Duret-Lutz's avatar Alexandre Duret-Lutz
Browse files

remfin: make sure Rabin automata are always converted to Büchi

Because using multiple acceptance condition is pointless in this case.

* src/twaalgos/remfin.cc (ra_to_ba): Extract most of the RA->BA code
into this new function for clarity.
* src/tests/remfin.test: Adjust.
parent 4bef219d
......@@ -323,7 +323,8 @@ HOA: v1
States: 15
Start: 13
AP: 2 "p1" "p0"
Acceptance: 2 Inf(1) | Inf(0)
acc-name: Buchi
Acceptance: 1 Inf(0)
properties: trans-labels explicit-labels state-acc
--BODY--
State: 0 {0}
......@@ -398,7 +399,7 @@ State: 13
[0&!1] 11
[!0&1] 2
[0&1] 3
State: 14 {1}
State: 14 {0}
[!0&1] 14
[0&1] 14
--END--
......
......@@ -47,11 +47,12 @@ namespace spot
// pairs (Fᵢ, Iᵢ), either no states from Iᵢ are visited or some
// states from Fᵢ are visited. (This corresponds to an accepting
// cycle with Streett acceptance.)
bool is_scc_ba_type(const const_twa_graph_ptr& aut,
const std::vector<unsigned>& states,
std::vector<bool>& final,
acc_cond::mark_t inf,
acc_cond::mark_t sets)
static bool
is_scc_ba_type(const const_twa_graph_ptr& aut,
const std::vector<unsigned>& states,
std::vector<bool>& final,
acc_cond::mark_t inf,
acc_cond::mark_t sets)
{
// Consider the SCC as one large cycle and check its
// intersection with all Fᵢs and Iᵢs: This is the SETS
......@@ -116,7 +117,7 @@ namespace spot
{
for (auto s: si.states_of(scc))
unknown.erase(s);
if (si.is_trivial(scc))
if (si.is_rejecting_scc(scc)) // this includes trivial SCCs
continue;
if (!is_scc_ba_type(aut, si.states_of(scc),
final, inf, si.acc(scc)))
......@@ -124,8 +125,145 @@ namespace spot
}
}
return true;
}
}
// Specialized conversion from Rabin acceptance to Büchi acceptance.
// Is able to detect SCCs that are Büchi-type (i.e., they can be
// converted to Büchi acceptance without chaning their structure).
// Currently only work with state-based acceptance.
//
// See "Deterministic ω-automata vis-a-vis Deterministic Büchi
// Automata", S. Krishnan, A. Puri, and R. Brayton (ISAAC'94) for
// some details about detecting Büchi-typeness.
//
// We essentially apply this method SCC-wise. The paper is
// concerned about *deterministic* automata, but we apply the
// algorithm on non-deterministic automata as well: in the worst
// case it is possible that a Büchi-type SCC with some
// non-deterministic has one accepting and one rejecting run for
// the same word. In this case we may fail to detect the
// Büchi-typeness of the SCC, but the resulting automaton should
// be correct nonetheless.
static twa_graph_ptr
ra_to_ba(const const_twa_graph_ptr& aut)
{
assert(aut->has_state_based_acc());
assert(aut->acc().is_rabin() > 0);
scc_info si(aut);
// For state-based Rabin automata, we check each SCC for
// BA-typeness. If an SCC is BA-type, its final states are stored
// in BA_FINAL_STATES.
std::vector<bool> scc_is_ba_type(si.scc_count(), false);
bool ba_type = false;
std::vector<bool> ba_final_states;
acc_cond::mark_t fin;
acc_cond::mark_t inf;
std::tie(inf, fin) = aut->get_acceptance().used_inf_fin_sets();
assert((fin << 1) == inf);
ba_final_states.resize(aut->num_states(), false);
ba_type = true; // until proven otherwise
unsigned scc_max = si.scc_count();
for (unsigned scc = 0; scc < scc_max; ++scc)
{
if (si.is_rejecting_scc(scc)) // this includes trivial SCCs
{
scc_is_ba_type[scc] = true;
continue;
}
bool scc_ba_type =
is_scc_ba_type(aut, si.states_of(scc),
ba_final_states, inf, si.acc(scc));
ba_type &= scc_ba_type;
scc_is_ba_type[scc] = scc_ba_type;
}
#if TRACE
trace << "SCC DBA-realizibility\n";
for (unsigned scc = 0; scc < scc_max; ++scc)
{
trace << scc << ": " << scc_is_ba_type[scc] << " {";
for (auto s: si.states_of(scc))
trace << ' ' << s;
trace << " }\n";
}
#endif
unsigned nst = aut->num_states();
auto res = make_twa_graph(aut->get_dict());
res->copy_ap_of(aut);
res->prop_copy(aut, { true, false, false, true });
res->new_states(nst);
auto final_acc = res->set_buchi();
res->set_init_state(aut->get_init_state_number());
std::vector<unsigned> state_map(aut->num_states());
for (unsigned n = 0; n < scc_max; ++n)
{
auto states = si.states_of(n);
if (scc_is_ba_type[n])
{
// If the SCC is BA-type, we know exactly what state need to
// be marked as accepting.
for (auto s: states)
{
acc_cond::mark_t acc = 0U;
if (ba_final_states[s])
acc = final_acc;
for (auto& t: aut->out(s))
res->new_edge(s, t.dst, t.cond, acc);
}
continue;
}
else
{
// The main copy is unaccepting
for (auto s: states)
for (auto& t: aut->out(s))
res->new_edge(s, t.dst, t.cond);
auto rem = si.acc(n) & fin;
if (!rem)
// No Fin sets used in this SCC.
continue;
auto sets = rem.sets();
unsigned ss = states.size();
for (auto r: sets)
{
unsigned base = res->new_states(ss);
for (auto s: states)
state_map[s] = base++;
for (auto s: states)
{
auto ns = state_map[s];
acc_cond::mark_t acc = aut->state_acc_sets(s);
if (acc.has(r))
continue;
for (auto& t: aut->out(s))
{
if (si.scc_of(t.dst) != n)
continue;
auto nd = state_map[t.dst];
res->new_acc_edge(ns, nd, t.cond, t.acc.has(r + 1));
// We need only one non-deterministic jump per
// cycle. As an approximation, we only do
// them on back-links.
if (t.dst <= s)
res->new_edge(s, nd, t.cond);
}
}
}
}
}
res->purge_dead_states();
return res;
}
// If the DNF is
// Fin(1)&Inf(2)&Inf(4) | Fin(2)&Fin(3)&Inf(1) |
......@@ -211,49 +349,8 @@ namespace spot
if (!aut->acc().uses_fin_acceptance())
return std::const_pointer_cast<twa_graph>(aut);
scc_info si(aut);
// For state-based Rabin automata, we check each SCC for
// BA-typeness. If an SCC is BA-type, its final states are stored
// in BA_FINAL_STATES.
std::vector<bool> scc_is_ba_type(si.scc_count(), false);
bool ba_type = false;
std::vector<bool> ba_final_states;
if (aut->has_state_based_acc()
&& aut->is_deterministic()
&& aut->acc().is_rabin() > 0)
{
acc_cond::mark_t fin;
acc_cond::mark_t inf;
std::tie(inf, fin) = aut->get_acceptance().used_inf_fin_sets();
assert((fin << 1) == inf);
ba_final_states.resize(aut->num_states(), false);
ba_type = true; // until proven otherwise
unsigned scc_max = si.scc_count();
for (unsigned scc = 0; scc < scc_max; ++scc)
{
if (si.is_trivial(scc))
{
scc_is_ba_type[scc] = true;
continue;
}
bool scc_ba_type =
is_scc_ba_type(aut, si.states_of(scc),
ba_final_states, inf, si.acc(scc));
ba_type &= scc_ba_type;
scc_is_ba_type[scc] = scc_ba_type;
}
#if TRACE
trace << "SCC DBA-realizibility\n";
for (unsigned scc = 0; scc < scc_max; ++scc)
{
trace << scc << ": " << scc_is_ba_type[scc] << " {";
for (auto s: si.states_of(scc))
trace << ' ' << s;
trace << " }\n";
}
#endif
}
if (aut->has_state_based_acc() && aut->acc().is_rabin() > 0)
return ra_to_ba(aut);
std::vector<acc_cond::acc_code> code;
std::vector<acc_cond::mark_t> rem;
......@@ -264,7 +361,6 @@ namespace spot
acc_cond::mark_t allfin = 0U;
{
auto acccode = aut->get_acceptance();
if (!acccode.is_dnf())
acccode = acccode.to_dnf();
......@@ -394,9 +490,6 @@ namespace spot
for (auto c: code)
new_code.append_or(std::move(c));
// The condition to use for SCCs that are BA-type.
acc_cond::mark_t final_acc = allinf.lowest();
unsigned cs = code.size();
for (unsigned i = 0; i < cs; ++i)
trace << i << " Rem " << rem[i] << " Code " << code[i]
......@@ -410,6 +503,8 @@ namespace spot
res->set_acceptance(aut->num_sets() + extra_sets, new_code);
res->set_init_state(aut->get_init_state_number());
scc_info si(aut);
unsigned nscc = si.scc_count();
std::vector<unsigned> state_map(nst);
for (unsigned n = 0; n < nscc; ++n)
......@@ -419,22 +514,6 @@ namespace spot
trace << "SCC #" << n << " uses " << m << '\n';
// What to keep and add into the main copy
if (scc_is_ba_type[n])
{
// If the SCC is BA-type, we know exactly what state need to
// be marked as accepting.
for (auto s: states)
{
acc_cond::mark_t acc = 0U;
if (ba_final_states[s])
acc = final_acc;
for (auto& t: aut->out(s))
res->new_edge(s, t.dst, t.cond, acc);
}
continue;
}
acc_cond::mark_t main_sets = 0U;
acc_cond::mark_t main_add = 0U;
bool intersects_fin = false;
......@@ -495,9 +574,6 @@ namespace spot
}
}
if (ba_type)
res->prop_state_based_acc();
res->purge_dead_states();
trace << "before cleanup: " << res->get_acceptance() << '\n';
cleanup_acceptance_here(res);
......
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