Rename is_safety_automaton() as is_guarantee_automaton() and

implement is_safety_mwdba().

Note: I swapped the name of safety and guarantee when I
implemented is_safety_automaton() on 2010-03-20.  Fortunately,
is_safety_automaton() was only used where is_guarantee_automaton()
would have been correct.

* src/tgbaalgos/safety.cc (is_guarantee_automaton): Rename as ...
(is_guarantee_automaton): ... this.
(is_safety_mwdba): New function.
* src/tgbaalgos/safety.hh: Adjust and add documentation.
* src/tgbaalgos/minimize.cc: Use is_guarantee_automaton() instead
of is_safety_automaton().
* src/tgbatests/safety.test: Rename as ...
* src/tgbatests/obligation.test: ... this, and augment the
test.
* src/tgbatest/Makefile.am: Adjust.
* src/tgbatest/ltl2tgba.cc (-O): Display whether a formula
represent a safety, guarantee, or obligation property.
* NEWS: Adjust.

src/tgbaalgos/safety.cc

@@ -19,11 +19,13 @@
 // 02111-1307, USA.
 
 #include "safety.hh"
+#include "misc/hash.hh"
+#include <deque>
 
 namespace spot
 {
   bool
-  is_safety_automaton(const tgba* aut, const scc_map* sm)
+  is_guarantee_automaton(const tgba* aut, const scc_map* sm)
   {
     // Create an scc_map of the user did not give one to us.
     bool need_sm = !sm;
@@ -69,6 +71,60 @@ namespace spot
     return result;
   }
 
+  bool is_safety_mwdba(const tgba* aut)
+  {
+    typedef Sgi::hash_set<const state*,
+			  state_ptr_hash, state_ptr_equal> seen_map;
+    seen_map seen;		   // States already seen.
+    std::deque<const state*> todo; // A queue of states yet to explore.
+
+    {
+      state* s = aut->get_init_state();
+      todo.push_back(s);
+      seen.insert(s);
+    }
+
+    bdd all_acc = aut->all_acceptance_conditions();
+
+    bool all_accepting = true;
+    while (all_accepting && !todo.empty())
+      {
+	const state* s = todo.front();
+	todo.pop_front();
+
+	tgba_succ_iterator* it = aut->succ_iter(s);
+	for (it->first(); !it->done(); it->next())
+	  {
+	    bdd acc = it->current_acceptance_conditions();
+	    if (acc != all_acc)
+	      {
+		all_accepting = false;
+		break;
+	      }
+	    state* d = it->current_state();
+	    if (seen.find(d) != seen.end())
+	      {
+		d->destroy();
+	      }
+	    else
+	      {
+		seen.insert(d);
+		todo.push_back(d);
+	      }
+	  }
+	delete it;
+      }
+
+    seen_map::const_iterator it = seen.begin();
+    while (it != seen.end())
+      {
+	seen_map::const_iterator old = it;
+	++it;
+	(*old)->destroy();
+      }
+
+    return all_accepting;
+  }