1 files changed, 67 insertions, 0 deletions
diff --git a/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/NotNodeReorderer.java b/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/NotNodeReorderer.java
new file mode 100644
index 00000000000..bd7339581f4
--- /dev/null
+++ b/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/NotNodeReorderer.java
@@ -0,0 +1,67 @@
+// Copyright 2016 Yahoo Inc. 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 magnarn
+ * @author bjorncs
+ */
+public class NotNodeReorderer implements PredicateProcessor {
+    /**
+     * @return 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;
+    }
+}