sketch mbi

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

src/qe/qe_mbi.cpp

@@ -0,0 +1,62 @@
+/*++
+Copyright (c) 2018 Microsoft Corporation
+
+Module Name:
+
+    qe_mbi.cpp
+
+Abstract:
+
+    Model-based interpolation utilities
+
+Author:
+
+    Nikolaj Bjorner (nbjorner), Arie Gurfinkel 2018-6-8
+
+Revision History:
+
+
+--*/
+
+
+namespace qe {
+    
+    lbool interpolator::binary(mbi_plugin& a, mbi_plugin& b, func_decl_ref_vector const& vars, expr_ref& itp) {
+        ast_manager& m = vars.get_manager();
+        model_ref mdl;
+        literal_vector lits(m);
+        bool a_turn = true;
+        expr_ref_vector itp_a(m), itp_b(m);
+        mbi_result last_res = mbi_undef;
+        while (true) {
+            auto* t1 = a_turn ? &a : &b;
+            auto* t2 = a_turn ? &b : &a;
+            mbi_result next_res = (*t1)(vars, lits, mdl);
+            switch (next_res) {
+            case mbi_sat:     
+                if (last_res == mbi_sat) {
+                    itp = nullptr;
+                    return l_true;
+                }
+                break; // continue
+            case mbi_unsat:
+                if (last_res == mbi_unsat) {
+                    // TBD, extract the interpolants
+                    // of what was blocked.
+                    return l_false;
+                }
+                t2->block(lits);
+                lits.reset();  // or find a prefix of lits?
+                next_res = mbi_undef;
+                a_turn = !a_turn;
+                break;
+            case mbi_augment:
+                a_turn = !a_turn;
+                break;
+            case mbi_undef:
+                return l_undef;                    
+            }
+            last_res = next_res;
+        }
+    }
+};