pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / contrib / facet / src / java / org / apache / lucene / util / encoding / DGapIntEncoder.java

diff --git a/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/DGapIntEncoder.java b/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/DGapIntEncoder.java
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+package org.apache.lucene.util.encoding;
+
+import java.io.IOException;
+import java.io.OutputStream;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * An {@link IntEncoderFilter} which encodes the gap between the given values,
+ * rather than the values themselves. This encoder usually yields better
+ * encoding performance space-wise (i.e., the final encoded values consume less
+ * space) if the values are 'close' to each other.
+ * <p>
+ * <b>NOTE:</b> this encoder assumes the values are given to
+ * {@link #encode(int)} in an ascending sorted manner, which ensures only
+ * positive values are encoded and thus yields better performance. If you are
+ * not sure whether the values are sorted or not, it is possible to chain this
+ * encoder with {@link SortingIntEncoder} to ensure the values will be
+ * sorted before encoding.
+ * 
+ * @lucene.experimental
+ */
+public class DGapIntEncoder extends IntEncoderFilter {
+
+  private int prev = 0;
+
+  /** Initializes with the given encoder. */
+  public DGapIntEncoder(IntEncoder encoder) {
+    super(encoder);
+  }
+
+  @Override
+  public void encode(int value) throws IOException {
+    encoder.encode(value - prev);
+    prev = value;
+  }
+
+  @Override
+  public IntDecoder createMatchingDecoder() {
+    return new DGapIntDecoder(encoder.createMatchingDecoder());
+  }
+  
+  @Override
+  public void reInit(OutputStream out) {
+    super.reInit(out);
+    prev = 0;
+  }
+
+  @Override
+  public String toString() {
+    return "DGap (" + encoder.toString() + ")";
+  }
+  
+}