pylucene 3.5.0-3

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

diff --git a/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/ChunksIntEncoder.java b/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/ChunksIntEncoder.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 IntEncoder} which encodes values in chunks. Implementations of this
+ * class assume the data which needs encoding consists of small, consecutive
+ * values, and therefore the encoder is able to compress them better. You can
+ * read more on the two implementations {@link FourFlagsIntEncoder} and
+ * {@link EightFlagsIntEncoder}.
+ * <p>
+ * Extensions of this class need to implement {@link #encode(int)} in order to
+ * build the proper indicator (flags). When enough values were accumulated
+ * (typically the batch size), extensions can call {@link #encodeChunk()} to
+ * flush the indicator and the rest of the values.
+ * <p>
+ * <b>NOTE:</b> flags encoders do not accept values &le; 0 (zero) in their
+ * {@link #encode(int)}. For performance reasons they do not check that
+ * condition, however if such value is passed the result stream may be corrupt
+ * or an exception will be thrown. Also, these encoders perform the best when
+ * there are many consecutive small values (depends on the encoder
+ * implementation). If that is not the case, the encoder will occupy 1 more byte
+ * for every <i>batch</i> number of integers, over whatever
+ * {@link VInt8IntEncoder} would have occupied. Therefore make sure to check
+ * whether your data fits into the conditions of the specific encoder.
+ * <p>
+ * For the reasons mentioned above, these encoders are usually chained with
+ * {@link UniqueValuesIntEncoder} and {@link DGapIntEncoder} in the following
+ * manner: <code><pre>
+ * IntEncoder fourFlags = 
+ *         new SortingEncoderFilter(new UniqueValuesIntEncoder(new DGapIntEncoder(new FlagsIntEncoderImpl())));
+ * </code></pre>
+ * 
+ * @lucene.experimental
+ */
+public abstract class ChunksIntEncoder extends IntEncoder {
+
+  /** Holds the values which must be encoded, outside the indicator. */
+  protected final int[] encodeQueue;
+  protected int encodeQueueSize = 0;
+
+  /** Encoder used to encode values outside the indicator. */
+  protected final IntEncoder encoder = new VInt8IntEncoder();
+
+  /** Represents bits flag byte. */
+  protected int indicator = 0;
+
+  /** Counts the current ordinal of the encoded value. */
+  protected byte ordinal = 0;
+
+  protected ChunksIntEncoder(int chunkSize) {
+    encodeQueue = new int[chunkSize];
+  }
+
+  /**
+   * Encodes the values of the current chunk. First it writes the indicator, and
+   * then it encodes the values outside the indicator.
+   */
+  protected void encodeChunk() throws IOException {
+    out.write(indicator);
+    for (int i = 0; i < encodeQueueSize; ++i) {
+      encoder.encode(encodeQueue[i]);
+    }
+    encodeQueueSize = 0;
+    ordinal = 0;
+    indicator = 0;
+  }
+
+  @Override
+  public void close() throws IOException {
+    if (ordinal != 0) {
+      encodeChunk();
+    }
+    encoder.close();
+    super.close();
+  }
+
+  @Override
+  public void reInit(OutputStream out) {
+    encoder.reInit(out);
+    super.reInit(out);
+    ordinal = 0;
+    indicator = 0;
+    encodeQueueSize = 0;
+  }
+
+}