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tgba_digraph: speedup purge_unreachable_states slightly

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* src/tgba/tgbagraph.cc (purge_unreachable_states): Rewrite using
only one vector.
This commit is contained in:
Alexandre Duret-Lutz 2014-10-30 09:59:57 +01:00
parent f0fd654c1f
commit f35be908c8
1 changed files with 28 additions and 19 deletions
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47
src/tgba/tgbagraph.cc
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@ -65,35 +65,44 @@ namespace spot
void tgba_digraph::purge_unreachable_states() void tgba_digraph::purge_unreachable_states()
{ {
unsigned num_states = g_.num_states(); unsigned num_states = g_.num_states();
if (num_states == 0) if (SPOT_UNLIKELY(num_states == 0))
return; return;
std::vector<unsigned> seen(num_states, 0); // The TODO vector serves two purposes:
std::vector<unsigned> todo; // - it is a stack of state to process,
todo.reserve(num_states); // - it is a set of processed states.
todo.push_back(init_number_); // The lower 31 bits of each entry is a state on the stack. (The
seen[init_number_] = 1; // next usable entry on the stack is indicated by todo_pos.) The
auto todo_pos = todo.begin(); // 32th bit (i.e., the sign bit) of todo[x] indicates whether
while (todo_pos != todo.end()) // states number x has been seen.
std::vector<unsigned> todo(num_states, 0);
const unsigned seen = 1 << (sizeof(unsigned)*8-1);
const unsigned mask = seen - 1;
todo[0] = init_number_;
todo[init_number_] |= seen;
unsigned todo_pos = 1;
do
{ {
for (auto& t: g_.out(*todo_pos)) unsigned cur = todo[--todo_pos] & mask;
if (!seen[t.dst]) todo[todo_pos] ^= cur; // Zero the state
for (auto& t: g_.out(cur))
if (!(todo[t.dst] & seen))
{ {
seen[t.dst] = 1; todo[t.dst] |= seen;
todo.push_back(t.dst); todo[todo_pos++] |= t.dst;
} }
++todo_pos;
} }
while (todo_pos > 0);
// Now renumber each used state. // Now renumber each used state.
unsigned current = 0; unsigned current = 0;
for (auto& v: seen) for (auto& v: todo)
if (!v) if (!(v & seen))
v = -1U; v = -1U;
else else
v = current++; v = current++;
if (current == seen.size()) if (current == todo.size())
return; // No useless state. return; // No unreachable state.
init_number_ = seen[init_number_]; init_number_ = todo[init_number_];
g_.defrag_states(std::move(seen), current); g_.defrag_states(std::move(todo), current);
} }
void tgba_digraph::purge_dead_states() void tgba_digraph::purge_dead_states()