ec: Renault et al LPAR'13 emptiness check

In order to reuse the computation of the
intersection between kripke and twa efficiently,
we use template inheritance through the
"mixin templates" technique.

* spot/Makefile.am, spot/mc/Makefile.am,
spot/mc/ec.hh, spot/mc/unionfind.cc,
spot/mc/unionfind.hh: here.

spot/mc/unionfind.hh

@@ -0,0 +1,52 @@
+// -*- coding: utf-8 -*-
+// Copyright (C) 2015, 2016 Laboratoire de Recherche et
+// Developpement de l'Epita
+//
+// 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 3 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include <spot/misc/common.hh>
+#include <vector>
+
+namespace spot
+{
+
+  /// \brief This Union-Find data structure is a particular
+  /// union-find, dedicated for emptiness checks below, see ec.hh. The
+  /// key of this union-find is int. Moreover, we suppose that only
+  /// consecutive int are inserted. This union-find includes most of
+  /// the classical optimisations (IPC, LR, PC, MS).
+  class SPOT_API int_unionfind final
+  {
+  private:
+    // Store the parent relation, i.e. -1 or x < id.size()
+    std::vector<int> id;
+
+    // id of a specially managed partition of "dead" elements
+    const int DEAD = 0;
+
+    int root(int i);
+
+  public:
+    int_unionfind();
+    void makeset(int e);
+    bool unite(int e1, int e2);
+    void markdead(int e);
+    bool sameset(int e1, int e2);
+    bool isdead(int e);
+  };
+}