added chunk based backbone utility

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

src/test/cnf_backbones.cpp

@@ -50,8 +50,123 @@ static void display_model(sat::solver const & s) {
     std::cout << "\n";
 }
 
+static void display_status(lbool r) {
+    switch (r) {
+    case l_true: 
+        std::cout << "sat\n"; 
+        break;
+    case l_undef: 
+        std::cout << "unknown\n"; 
+        break;
+    case l_false: 
+        std::cout << "unsat\n"; 
+        break;
+    }
+}
 
-static void cnf_backbones(char const* file_name) {
+static void prune_unfixed(sat::literal_vector& lambda, sat::model const& m) {
+    for (unsigned i = 0; i < lambda.size(); ++i) {
+        if ((m[lambda[i].var()] == l_false) != lambda[i].sign()) {
+            lambda[i] = lambda.back();
+            lambda.pop_back();
+            --i;
+        }
+    }
+}
+
+// Algorithm 7: Corebased Algorithm with Chunking
+
+static void back_remove(sat::literal_vector& lits, sat::literal l) {
+    for (unsigned i = lits.size(); i > 0; ) {
+        --i;
+        if (lits[i] == l) {
+            lits[i] = lits.back();
+            lits.pop_back();
+            return;
+        }
+    }
+    std::cout << "UNREACHABLE\n";
+}
+
+static void brute_force_consequences(sat::solver& s, sat::literal_vector const& gamma, sat::literal_vector& backbones) {
+    for (unsigned i = 0; i < gamma.size(); ++i) {
+        sat::literal nlit = ~gamma[i];
+        lbool r = s.check(1, &nlit);
+        if (r == l_false) {
+            backbones.push_back(gamma[i]);
+        }
+    }
+}
+
+static lbool core_chunking(sat::solver& s, sat::bool_var_vector& vars, vector<sat::literal_vector>& conseq, unsigned K) {
+    lbool r = s.check();
+    display_status(r);
+    if (r != l_true) {
+        return r;
+    }
+    sat::model const & m = s.get_model();
+    sat::literal_vector lambda, backbones;
+    for (unsigned i = 1; i < m.size(); i++) {
+        lambda.push_back(sat::literal(i, m[i] == l_false));
+    }
+    while (!lambda.empty()) {
+        IF_VERBOSE(1, verbose_stream() << "(sat-backbone-core " << lambda.size() << " " << backbones.size() << ")\n";);
+        unsigned k = std::min(K, lambda.size());
+        sat::literal_vector gamma, omegaN;
+        for (unsigned i = 0; i < k; ++i) {
+            sat::literal l = lambda[lambda.size() - i - 1];
+            gamma.push_back(l);
+            omegaN.push_back(~l);
+        }
+        while (true) {
+            r = s.check(omegaN.size(), omegaN.c_ptr());
+            if (r == l_true) {
+                IF_VERBOSE(1, verbose_stream() << "(sat) " << omegaN << "\n";);
+                prune_unfixed(lambda, s.get_model());
+                break;
+            }
+            sat::literal_vector const& core = s.get_core();
+            sat::literal_vector occurs;
+            IF_VERBOSE(1, verbose_stream() << "(core " << core.size() << ")\n";);
+            for (unsigned i = 0; i < omegaN.size(); ++i) {
+                if (core.contains(omegaN[i])) {
+                    occurs.push_back(omegaN[i]);
+                }
+            }
+            if (occurs.size() == 1) {
+                sat::literal lit = occurs.back();
+                sat::literal nlit = ~lit;
+                backbones.push_back(~lit);
+                back_remove(lambda, ~lit);
+                back_remove(gamma, ~lit);
+                s.mk_clause(1, &nlit);
+            }
+            for (unsigned i = 0; i < omegaN.size(); ++i) {
+                if (occurs.contains(omegaN[i])) {
+                    omegaN[i] = omegaN.back();
+                    omegaN.pop_back();
+                    --i;
+                }
+            }
+            if (omegaN.empty() && occurs.size() > 1) {
+                brute_force_consequences(s, gamma, backbones);
+                for (unsigned i = 0; i < gamma.size(); ++i) {
+                    back_remove(lambda, gamma[i]);
+                }
+                break;
+            }
+        }
+    }
+    for (unsigned i = 0; i < backbones.size(); ++i) {
+        sat::literal_vector cons;
+        cons.push_back(backbones[i]);
+        conseq.push_back(cons);
+    }
+    return l_true;
+}
+
+
+static void cnf_backbones(bool use_chunk, char const* file_name) {
     g_start_time = clock();
     register_on_timeout_proc(on_timeout);
     signal(SIGINT, on_ctrl_c);
@@ -81,26 +196,23 @@ static void cnf_backbones(char const* file_name) {
         vars.push_back(i);        
         solver.set_external(i);
     }
-    lbool r = solver.get_consequences(assumptions, vars, conseq);
-    
-    switch (r) {
-    case l_true: 
-        std::cout << "sat\n"; 
-        std::cout << vars.size() << " " << conseq.size() << "\n";
-        break;
-    case l_undef: 
-        std::cout << "unknown\n"; 
-        break;
-    case l_false: 
-        std::cout << "unsat\n"; 
-        break;
+    lbool r;
+    if (use_chunk) {
+        r = core_chunking(solver, vars, conseq, 100);
     }
+    else {
+        r = solver.get_consequences(assumptions, vars, conseq);
+    }
+    std::cout << vars.size() << " " << conseq.size() << "\n";
+    display_status(r);
     display_statistics();
 }
 
 void tst_cnf_backbones(char ** argv, int argc, int& i) {
     if (i + 1 < argc) {
-        cnf_backbones(argv[i + 1]);
+        bool use_chunk = (i + 2 < argc && argv[i + 2] == std::string("chunk"));
+        cnf_backbones(use_chunk, argv[i + 1]);
         ++i;
+        if (use_chunk) ++i;
     }
 }