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/********************* */
/*! \file propositional_query.cpp
** \verbatim
** Original author: taking
** Major contributors: mdeters
** Minor contributors (to current version): none
** This file is part of the CVC4 prototype.
** Copyright (c) 2009-2012 New York University and The University of Iowa
** See the file COPYING in the top-level source directory for licensing
** information.\endverbatim
**
** \brief A class for simple, quick, propositional
** satisfiability/validity checking
**
** PropositionalQuery is a way for parts of CVC4 to do quick purely
** propositional satisfiability or validity checks on a Node. These
** checks do no theory reasoning, and handle atoms as propositional
** variables, but can sometimes be useful for subqueries.
**/
#include "util/propositional_query.h"
#include <map>
#include <algorithm>
using namespace std;
using namespace CVC4;
using namespace CVC4::kind;
#ifdef CVC4_CUDD
#include <util.h>
#include <cudd.h>
#include <cuddObj.hh>
namespace CVC4 {
class BddInstance {
private:
Cudd d_mgr;
typedef std::map<Node, BDD> AtomToIDMap;
AtomToIDMap d_atomToBddMap;
unsigned d_atomId;
BDD encodeNode(TNode t);
BDD encodeAtom(TNode t);
BDD encodeCombinator(TNode t);
bool isAnAtom(TNode t) {
switch(t.getKind()) {
case NOT:
case XOR:
case IFF:
case IMPLIES:
case OR:
case AND:
return false;
case ITE:
return t.getType().isBoolean();
default:
return true;
}
}
void setupAtoms(TNode t);
void clear() {
d_atomId = 0;
d_atomToBddMap.clear();
}
Result d_result;
public:
static const unsigned MAX_VARIABLES = 20;
BddInstance(TNode t) : d_atomToBddMap(), d_atomId(0) {
setupAtoms(t);
Debug("bdd::sat") << t << endl;
Debug("bdd::sat") << d_atomToBddMap.size() << endl;
if(d_atomToBddMap.size() > MAX_VARIABLES) {
d_result = Result(Result::SAT_UNKNOWN, Result::TIMEOUT);
} else {
BDD res = encodeNode(t);
BDD falseBdd = d_mgr.bddZero();
bool isUnsat = (res == falseBdd);
clear();
if(isUnsat) {
d_result = Result::UNSAT;
} else {
d_result = Result::SAT;
}
}
}
Result getResult() const { return d_result; }
};/* class BddInstance */
}/* CVC4 namespace */
BDD BddInstance::encodeNode(TNode t) {
if(isAnAtom(t)) {
return encodeAtom(t);
} else {
return encodeCombinator(t);
}
}
BDD BddInstance::encodeCombinator(TNode t) {
switch(t.getKind()) {
case XOR: {
Assert(t.getNumChildren() == 2);
return encodeNode(t[0]).Xor(encodeNode(t[1]));
}
case IFF: {
Assert(t.getNumChildren() == 2);
BDD left = encodeNode(t[0]);
BDD right = encodeNode(t[1]);
return (!left | right) & (left | !right);
}
case IMPLIES: {
Assert(t.getNumChildren() == 2);
BDD left = encodeNode(t[0]);
BDD right = encodeNode(t[1]);
return (!left | right);
}
case AND:
case OR: {
Assert(t.getNumChildren() >= 2);
TNode::iterator i = t.begin(), end = t.end();
BDD tmp = encodeNode(*i);
++i;
for(; i != end; ++i) {
BDD curr = encodeNode(*i);
if(t.getKind() == AND) {
tmp = tmp & curr;
} else {
tmp = tmp | curr;
}
}
return tmp;
}
case ITE: {
Assert(t.getType().isBoolean());
BDD cnd = encodeNode(t[0]);
BDD thenBranch = encodeNode(t[1]);
BDD elseBranch = encodeNode(t[2]);
return cnd.Ite(thenBranch, elseBranch);
}
case NOT:
return ! encodeNode(t[0]);
default:
Unhandled(t.getKind());
}
}
BDD BddInstance::encodeAtom(TNode t) {
if(t.getKind() == kind::CONST_BOOLEAN) {
if(t.getConst<bool>()) {
return d_mgr.bddOne();
} else {
return d_mgr.bddZero();
}
}
Assert(t.getKind() != kind::CONST_BOOLEAN);
AtomToIDMap::iterator findT = d_atomToBddMap.find(t);
Assert(d_atomToBddMap.find(t) != d_atomToBddMap.end());
return findT->second;
}
void BddInstance::setupAtoms(TNode t) {
if(t.getKind() == kind::CONST_BOOLEAN) {
// do nothing
} else if(isAnAtom(t)) {
AtomToIDMap::iterator findT = d_atomToBddMap.find(t);
if(findT == d_atomToBddMap.end()) {
BDD var = d_mgr.bddVar();
d_atomToBddMap.insert(make_pair(t, var));
d_atomId++;
}
} else {
for(TNode::iterator i = t.begin(), end = t.end(); i != end; ++i) {
setupAtoms(*i);
}
}
}
Result PropositionalQuery::isSatisfiable(TNode q) {
BddInstance instance(q);
return instance.getResult();
}
Result PropositionalQuery::isTautology(TNode q) {
Node negQ = q.notNode();
Result satResult = isSatisfiable(negQ);
return satResult.asValidityResult();
}
#else /* CVC4_CUDD */
// if CUDD wasn't available at build time, just return UNKNOWN everywhere.
Result PropositionalQuery::isSatisfiable(TNode q) {
return Result(Result::SAT_UNKNOWN, Result::UNSUPPORTED);
}
Result PropositionalQuery::isTautology(TNode q) {
return Result(Result::VALIDITY_UNKNOWN, Result::UNSUPPORTED);
}
#endif /* CVC4_CUDD */
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