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remove_fin: remove useless states

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* src/tgba/tgbagraph.cc (purge_dead_states): Using a DFS to compute a
topological order, allowing to remove useless using a second
pass (instead of iterating the passes until there is nothing to remove).
* src/tgbaalgos/remfin.cc: Call purge_dead_states().
* src/tgbatest/remfin.test, src/tgbatest/det.test: Adjust expected
output.
* doc/org/autfilt.org: Update example.
This commit is contained in:
Alexandre Duret-Lutz 2015-03-24 12:04:30 +01:00
parent b4e22a3c7e
commit 020bbd4473
5 changed files with 82 additions and 93 deletions
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96
src/tgba/tgbagraph.cc
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@ -178,52 +178,74 @@ namespace spot
unsigned num_states = g_.num_states();
if (num_states == 0)
return;
std::vector<unsigned> info(num_states, 0);
// In this loop, info[s] means that the state is useless.
bool untouched;
std::vector<unsigned> useful(num_states, 0);
// Make a DFS to compute a topological order.
std::vector<unsigned> order;
order.reserve(num_states);
std::vector<std::pair<unsigned, unsigned>> todo; // state, trans
useful[init_number_] = 1;
todo.emplace_back(init_number_, g_.state_storage(init_number_).succ);
do
{
untouched = true;
for (unsigned s = 0; s < num_states; ++s)
unsigned src;
unsigned tid;
std::tie(src, tid) = todo.back();
if (tid == 0U)
{
if (info[s])
continue;
bool useless = true;
auto t = g_.out_iteraser(s);
while (t)
{
// Erase any transition to a unused state.
if (info[t->dst])
{
t.erase();
continue;
}
// if we have a transition, to a used state,
// then the state is useful.
useless = false;
++t;
}
if (useless)
{
info[s] = true;
untouched = false;
}
todo.pop_back();
order.push_back(src);
continue;
}
auto& t = g_.trans_storage(tid);
todo.back().second = t.next_succ;
unsigned dst = t.dst;
if (useful[dst] != 1)
{
todo.emplace_back(dst, g_.state_storage(dst).succ);
useful[dst] = 1;
}
}
while (!untouched);
while (!todo.empty());
// Process states in topological order
for (auto s: order)
{
auto t = g_.out_iteraser(s);
bool useless = true;
while (t)
{
// Erase any transition to a useless state.
if (!useful[t->dst])
{
t.erase();
continue;
}
// if we have a transition to a useful state, then the
// state is useful.
useless = false;
++t;
}
if (useless)
useful[s] = 0;
}
// Make sure the initial state is useful (even if it has been
// marked as useless by the previous loop because it has no
// successor).
useful[init_number_] = 1;
// Assume that the initial state is useful.
info[init_number_] = false;
// Now renumber each used state.
unsigned current = 0;
for (auto& v: info)
if (v)
v = -1U;
for (unsigned s = 0; s < num_states; ++s)
if (useful[s])
useful[s] = current++;
else
v = current++;
if (current == info.size())
useful[s] = -1U;
if (current == num_states)
return; // No useless state.
init_number_ = info[init_number_];
g_.defrag_states(std::move(info), current);
init_number_ = useful[init_number_];
g_.defrag_states(std::move(useful), current);
}
}