adding parallel threads

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/sat/sat_par.h

@@ -0,0 +1,39 @@
+/*++
+Copyright (c) 2017 Microsoft Corporation
+
+Module Name:
+
+    sat_par.h
+
+Abstract:
+
+    Utilities for parallel SAT solving.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2017-1-29.
+
+Revision History:
+
+--*/
+#ifndef SAT_PAR_H_
+#define SAT_PAR_H_
+
+#include"sat_types.h"
+#include"hashtable.h"
+#include"map.h"
+
+namespace sat {
+
+    class par {
+        typedef hashtable<unsigned, u_hash, u_eq> index_set;
+        literal_vector m_units;
+        index_set      m_unit_set;
+    public:
+        par();
+        void exchange(literal_vector const& in, unsigned& limit, literal_vector& out);
+    };
+
+};
+
+#endif