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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.search.predicate.optimization;
import com.yahoo.document.predicate.Conjunction;
import com.yahoo.document.predicate.Disjunction;
import com.yahoo.document.predicate.Negation;
import com.yahoo.document.predicate.Predicate;
import java.util.ArrayList;
import java.util.List;
/**
* Reorders not nodes to improve the efficiency of the z-star posting list compression.
* It puts negative children first in AND-nodes, and last in OR-nodes.
*
* @author Magnar Nedland
* @author bjorncs
*/
public class NotNodeReorderer implements PredicateProcessor {
/**
* Returns true if the predicate ends in a negation.
*/
public boolean processSubTree(Predicate predicate) {
if (predicate == null) {
return false;
}
if (predicate instanceof Negation) {
// All negations are for leaf-nodes after AndOrSimplifier has run.
return true;
} else if (predicate instanceof Conjunction) {
List<Predicate> in = ((Conjunction)predicate).getOperands();
List<Predicate> out = new ArrayList<>(in.size());
List<Predicate> positiveChildren = new ArrayList<>(in.size());
for (Predicate operand : in) {
if (processSubTree(operand)) {
out.add(operand);
} else {
positiveChildren.add(operand);
}
}
out.addAll(positiveChildren);
((Conjunction)predicate).setOperands(out);
return positiveChildren.isEmpty();
} else if (predicate instanceof Disjunction) {
List<Predicate> in = ((Disjunction)predicate).getOperands();
List<Predicate> out = new ArrayList<>(in.size());
List<Predicate> negativeChildren = new ArrayList<>(in.size());
for (Predicate operand : in) {
if (processSubTree(operand)) {
negativeChildren.add(operand);
} else {
out.add(operand);
}
}
out.addAll(negativeChildren);
((Disjunction)predicate).setOperands(out);
return !negativeChildren.isEmpty();
}
return false;
}
@Override
public Predicate process(Predicate predicate, PredicateOptions options) {
processSubTree(predicate);
return predicate;
}
}
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