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/********************* -*- C++ -*- */
/** cnf_converter.h
** Original author: mdeters
** Major contributors: dejan
** Minor contributors (to current version): none
** This file is part of the CVC4 prototype.
** Copyright (c) 2009 The Analysis of Computer Systems Group (ACSys)
** Courant Institute of Mathematical Sciences
** New York University
** See the file COPYING in the top-level source directory for licensing
** information.
**
** A CNF converter for CVC4.
**/
#ifndef __CVC4__SMT__CNF_CONVERTER_H
#define __CVC4__SMT__CNF_CONVERTER_H
#include "expr/node_builder.h"
#include "expr/node.h"
#include "smt/cnf_conversion.h"
#include <map>
namespace CVC4 {
namespace smt {
class CnfConverter {
private:
/** Our node manager */
NodeManager *d_nm;
/** The type of conversion this converter performs */
CVC4::CnfConversion d_conversion;
/** Map of already-converted Nodes */
std::map<Node, Node> d_conversionMap;
/**
* Returns true iff the CNF conversion for the Node was cached
* previously.
*/
bool conversionMapped(const Node& n) {
return d_conversionMap.find(n) != d_conversionMap.end();
}
/**
* Returns true iff the CNF conversion for the Node was cached
* previously.
*/
Node getConversionMap(const Node& n) {
return d_conversionMap[n];
}
/**
* Cache a new CNF conversion.
*/
void mapConversion(const Node& n, const Node& m) {
d_conversionMap[n] = m;
}
/**
* Compress a NOT: do NNF transformation plus a bit. Does DNE,
* NOT FALSE ==> TRUE, NOT TRUE ==> FALSE, and pushes NOT inside
* of ANDs and ORs. Calls doConvert() on subnodes.
*/
Node compressNOT(const Node& e, NodeBuilder<>* sideConditions);
/**
* Flatten a Node of kind K. K here is going to be AND or OR.
* "Flattening" means to take all children of the Node with the same
* kind and hoist their children to the top-level. So e.g.
* (AND (AND x y) (AND (AND z)) w) ==> (AND x y z w).
*/
template <CVC4::Kind K>
Node flatten(const Node& e, NodeBuilder<>* sideConditions);
/**
* Do a direct CNF conversion (with possible exponential blow-up in
* the number of clauses). No new variables are introduced. The
* output is equivalent to the input.
*/
Node directConvert(const Node& e, NodeBuilder<>* sideConditions);
/**
* Helper method for "direct" CNF preprocessing. CNF-converts an OR.
*/
void directOrHelper(Node::iterator p,
Node::iterator end,
NodeBuilder<>& result,
NodeBuilder<>* sideConditions);
/**
* Do a satisfiability-preserving CNF conversion with variable
* introduction. Doesn't suffer from exponential blow-up in the
* number of clauses, but new variables are introduced and the
* output is equisatisfiable (but not equivalent) to the input.
*/
Node varIntroductionConvert(const Node& e, NodeBuilder<>* sideConditions);
/**
* Convert an expression into CNF. If a conversion already exists
* for the Node, it is returned. If a conversion doesn't exist, it
* is computed and returned (caching the result).
*/
Node doConvert(const Node& e, NodeBuilder<>* sideconditions);
public:
/**
* Construct a CnfConverter.
*/
CnfConverter(NodeManager* nm, CVC4::CnfConversion cnv = CNF_VAR_INTRODUCTION) :
d_nm(nm),
d_conversion(cnv) {}
/**
* Convert an expression into CNF. If a conversion already exists
* for the Node, it is returned. If a conversion doesn't exist, it
* is computed and returned (caching the result).
*/
Node convert(const Node& e);
};/* class CnfConverter */
template <CVC4::Kind K>
struct flatten_traits;
template <>
struct flatten_traits<AND> {
static const CVC4::Kind ignore = TRUE; // TRUE AND x == x
static const CVC4::Kind shortout = FALSE; // FALSE AND x == FALSE
};
template <>
struct flatten_traits<OR> {
static const CVC4::Kind ignore = FALSE; // FALSE OR x == x
static const CVC4::Kind shortout = TRUE; // TRUE OR x == TRUE
};
template <CVC4::Kind K>
Node CnfConverter::flatten(const Node& e, NodeBuilder<>* sideConditions) {
Assert(e.getKind() == K);
NodeBuilder<> n(K);
for(Node::iterator i = e.begin(); i != e.end(); ++i) {
Node f = doConvert(*i, sideConditions);
if(f.getKind() == K) {
for(Node::iterator j = f.begin(); j != f.end(); ++j) {
n << *j;
}
} else if(f.getKind() == flatten_traits<K>::ignore) {
/* do nothing */
} else if(f.getKind() == flatten_traits<K>::shortout) {
return f;
} else {
n << f;
}
}
return n;
}
}/* CVC4::smt namespace */
}/* CVC4 namespace */
#endif /* __CVC4__SMT__CNF_CONVERTER_H */
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