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/********************* */
/*! \file boolean_simplification.h
** \verbatim
** Original author: taking
** Major contributors: none
** Minor contributors (to current version): none
** This file is part of the CVC4 prototype.
** Copyright (c) 2009, 2010, 2011 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.\endverbatim
**
** \brief Simple routines for Boolean simplification
**
** Simple, commonly-used routines for Boolean simplification.
**/
#include "cvc4_private.h"
#ifndef __CVC4__BOOLEAN_SIMPLIFICATION_H
#define __CVC4__BOOLEAN_SIMPLIFICATION_H
#include <vector>
#include <algorithm>
#include "expr/node.h"
#include "util/Assert.h"
namespace CVC4 {
/**
* A class to contain a number of useful functions for simple
* simplification of nodes. One never uses it as an object (and
* it cannot be constructed). It is used as a namespace.
*/
class BooleanSimplification {
// cannot construct one of these
BooleanSimplification() CVC4_UNUSED;
BooleanSimplification(const BooleanSimplification&) CVC4_UNUSED;
static void push_back_associative_commute_recursive
(Node n, std::vector<Node>& buffer, Kind k, Kind notK, bool negateNode)
throw(AssertionException);
public:
/**
* The threshold for removing duplicates. (See removeDuplicates().)
*/
static const uint32_t DUPLICATE_REMOVAL_THRESHOLD = 10;
/**
* Remove duplicate nodes from a vector, modifying it in-place.
* If the vector has size >= DUPLICATE_REMOVAL_THRESHOLD, this
* function is a no-op.
*/
static void removeDuplicates(std::vector<Node>& buffer)
throw(AssertionException) {
if(buffer.size() < DUPLICATE_REMOVAL_THRESHOLD) {
std::sort(buffer.begin(), buffer.end());
std::vector<Node>::iterator new_end =
std::unique(buffer.begin(), buffer.end());
buffer.erase(new_end, buffer.end());
}
}
/**
* Takes a node with kind AND, collapses all AND and (NOT OR)-kinded
* children of it (as far as possible---see
* push_back_associative_commute()), removes duplicates, and returns
* the resulting Node.
*/
static Node simplifyConflict(Node andNode) throw(AssertionException) {
AssertArgument(!andNode.isNull(), andNode);
AssertArgument(andNode.getKind() == kind::AND, andNode);
std::vector<Node> buffer;
push_back_associative_commute(andNode, buffer, kind::AND, kind::OR);
removeDuplicates(buffer);
NodeBuilder<> nb(kind::AND);
nb.append(buffer);
return nb;
}
/**
* Takes a node with kind OR, collapses all OR and (NOT AND)-kinded
* children of it (as far as possible---see
* push_back_associative_commute()), removes duplicates, and returns
* the resulting Node.
*/
static Node simplifyClause(Node orNode) throw(AssertionException) {
AssertArgument(!orNode.isNull(), orNode);
AssertArgument(orNode.getKind() == kind::OR, orNode);
std::vector<Node> buffer;
push_back_associative_commute(orNode, buffer, kind::OR, kind::AND);
removeDuplicates(buffer);
NodeBuilder<> nb(kind::OR);
nb.append(buffer);
return nb;
}
/**
* Takes a node with kind IMPLIES, converts it to an OR, then
* simplifies the result with simplifyClause().
*
* The input doesn't actually have to be Horn, it seems, but that's
* the common case(?), hence the name.
*/
static Node simplifyHornClause(Node implication) throw(AssertionException) {
AssertArgument(implication.getKind() == kind::IMPLIES, implication);
TNode left = implication[0];
TNode right = implication[1];
Node notLeft = negate(left);
Node clause = NodeBuilder<2>(kind::OR) << notLeft << right;
return simplifyClause(clause);
}
/**
* Aids in reforming a node. Takes a node of (N-ary) kind k and
* copies its children into an output vector, collapsing its k-kinded
* children into it. Also collapses negations of notK. For example:
*
* push_back_associative_commute( [OR [OR a b] [OR b c d] [NOT [AND e f]]],
* buffer, kind::OR, kind::AND )
* yields a "buffer" vector of [a b b c d e f]
*
* @param n the node to operate upon
* @param buffer the output vector (must be empty on entry)
* @param k the kind to collapse (should equal the kind of node n)
* @param notK the "negation" of kind k (e.g. OR's negation is AND),
* or kind::UNDEFINED_KIND if none.
*/
static inline void
push_back_associative_commute(Node n, std::vector<Node>& buffer,
Kind k, Kind notK)
throw(AssertionException) {
AssertArgument(buffer.empty(), buffer);
AssertArgument(!n.isNull(), n);
AssertArgument(k != kind::UNDEFINED_KIND && k != kind::NULL_EXPR, k);
AssertArgument(notK != kind::NULL_EXPR, notK);
AssertArgument(n.getKind() == k, n,
"expected node to have kind %s", kindToString(k).c_str());
push_back_associative_commute_recursive(n, buffer, k, notK, false);
}/* push_back_associative_commute() */
/**
* Negates a node, doing all the double-negation elimination
* that's possible.
*
* @param n the node to negate (cannot be the null node)
*/
static Node negate(TNode n) throw(AssertionException) {
AssertArgument(!n.isNull(), n);
bool polarity = true;
TNode base = n;
while(base.getKind() == kind::NOT){
base = base[0];
polarity = !polarity;
}
if(polarity){
return base.notNode();
}else{
return base;
}
}
};/* class BooleanSimplification */
}/* CVC4 namespace */
#endif /* __CVC4__BOOLEAN_SIMPLIFICATION_H */
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