Improve SCC simplification by removing implied acceptance conditions.

Spot 0.7.1 used to need 190 acceptance conditions to translate the
188 literature formulae.  With this patch we are down to 185.
That's not an impressive, but there are only ~20 formulae that
require more than 1 acceptance conditions; hence little room for
improvement.

* src/misc/bddlt.hh (bdd_hash): New function.
* src/misc/accconv.hh, src/misc/accconv.cc: New files.
* src/misc/Makefile.am: Add them.
* src/tgbaalgos/scc.cc (scc_map::build_map): Adjust
to record all combination of acceptance conditions occurring in a SCC.
* src/tgbaalgos/scc.hh (scc_map::scc::useful_acc): Update description.
* src/tgbaalgos/sccfilter.cc (scc_filter): Simplify acceptance
conditions that are always implied by another acceptance
conditions.  Previously, we only removed acceptance conditions
that where always present in accepting SCCs.
* src/tgbatest/sccsimpl.test: New file.
* src/tgbatest/Makefile.am (TESTS): Add it.

src/misc/accconv.hh

@@ -0,0 +1,53 @@
+// Copyright (C) 2011 Laboratoire de Recherche et Developpement 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 2 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 Spot; see the file COPYING.  If not, write to the Free
+// Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+// 02111-1307, USA.
+
+#ifndef SPOT_MISC_ACCCONV_HH
+# define SPOT_MISC_ACCCONV_HH
+
+#include <bdd.h>
+#include "misc/hash.hh"
+#include "misc/bddlt.hh"
+
+namespace spot
+{
+  /// \brief Help class to convert between acceptance conditions to
+  /// other BDD formats.
+  class acceptance_convertor
+  {
+  public:
+    acceptance_convertor(bdd allneg)
+      : allneg_(allneg)
+    {
+    }
+
+    bdd as_positive_product(bdd acc);
+
+    bdd as_full_product(bdd acc);
+
+  protected:
+    bdd allneg_;
+    typedef Sgi::hash_map<bdd, bdd, bdd_hash> bdd_cache_t;
+    bdd_cache_t pos_prod_cache_;
+    bdd_cache_t full_prod_cache_;
+  };
+
+}
+
+#endif // SPOT_MISC_ACCCONV_HH