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// Copyright 2017 Yahoo Holdings. 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;
/**
* Simplifies a predicate by:
* - Combining child-AND/OR nodes with direct parents of the same type
* - Pushing negations down to leaf nodes by using De Morgan's law.
*
* @author magnarn
* @author bjorncs
*/
public class AndOrSimplifier implements PredicateProcessor {
public Predicate simplifySubTree(Predicate predicate, boolean negated) {
if (predicate == null) {
return null;
}
if (predicate instanceof Negation) {
return simplifySubTree(((Negation) predicate).getOperand(), !negated);
} else if (predicate instanceof Conjunction) {
List<Predicate> in = ((Conjunction)predicate).getOperands();
List<Predicate> out = new ArrayList<>(in.size());
for (Predicate operand : in) {
operand = simplifySubTree(operand, negated);
if (operand instanceof Conjunction) {
out.addAll(((Conjunction)operand).getOperands());
} else {
out.add(operand);
}
}
if (negated) {
return new Disjunction(out);
}
((Conjunction)predicate).setOperands(out);
} else if (predicate instanceof Disjunction) {
List<Predicate> in = ((Disjunction)predicate).getOperands();
List<Predicate> out = new ArrayList<>(in.size());
for (Predicate operand : in) {
operand = simplifySubTree(operand, negated);
if (operand instanceof Disjunction) {
out.addAll(((Disjunction)operand).getOperands());
} else {
out.add(operand);
}
}
if (negated) {
return new Conjunction(out);
}
((Disjunction)predicate).setOperands(out);
} else {
if (negated) {
return new Negation(predicate);
}
}
return predicate;
}
@Override
public Predicate process(Predicate predicate, PredicateOptions options) {
return simplifySubTree(predicate, false);
}
}
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