pylucene 3.5.0-3

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

diff --git a/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/FourFlagsIntEncoder.java b/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/FourFlagsIntEncoder.java
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+++ b/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/FourFlagsIntEncoder.java
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+package org.apache.lucene.util.encoding;
+
+import java.io.IOException;
+
+/**
+ * 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.
+ */
+
+/**
+ * A {@link ChunksIntEncoder} which encodes values in chunks of 4. Every group
+ * starts with a single byte (called indicator) which represents 4 - 2 bit
+ * flags, where the values:
+ * <ul>
+ * <li>1, 2 or 3 mean the encoded value is '1', '2' or '3' respectively.
+ * <li>0 means the value is encoded using {@link VInt8IntEncoder}, and the
+ * encoded bytes follow the indicator.<br>
+ * Since value 0 is illegal, and 1-3 are encoded in the indicator, the actual
+ * value that is encoded is <code>value-4</code>, which saves some more bits.
+ * </ul>
+ * Encoding example:
+ * <ul>
+ * <li>Original values: 6, 16, 5, 9, 7, 1, 11
+ * <li>After sorting: 1, 5, 6, 7, 9, 11, 16
+ * <li>D-Gap computing: 1, 4, 1, 1, 2, 5 (so far - done by
+ * {@link DGapIntEncoder})
+ * <li>Encoding: 1,0,1,1 as the first indicator, followed by 0 (4-4), than
+ * 2,0,0,0 as the second indicator, followed by 1 (5-4) encoded with.
+ * <li>Binary encode: <u>01 | 01 | 00 | 01</u> 00000000 <u>00 | 00 | 00 | 10</u>
+ * 00000001 (indicators are <u>underlined</u>).<br>
+ * <b>NOTE:</b> the order of the values in the indicator is lsb &rArr; msb,
+ * which allows for more efficient decoding.
+ * </ul>
+ * 
+ * @lucene.experimental
+ */
+public class FourFlagsIntEncoder extends ChunksIntEncoder {
+
+  /**
+   * Holds all combinations of <i>indicator</i> flags for fast encoding (saves
+   * time on bit manipulation @ encode time)
+   */
+  private static byte[][] encodeTable = new byte[][] {
+    new byte[] { 0x00, 0x00, 0x00, 0x00 },
+    new byte[] { 0x01, 0x04, 0x10, 0x40 },
+    new byte[] { 0x02, 0x08, 0x20, (byte) 0x80 },
+    new byte[] { 0x03, 0x0C, 0x30, (byte) 0xC0 },
+  };
+
+  public FourFlagsIntEncoder() {
+    super(4);
+  }
+
+  /**
+   * Small values (<=3) are stored in the <code>indicator</code> while larger
+   * values are saved for later encoding in the {@link #encodeQueue}. Since
+   * Vint8 will only encode values larger or equal to 4, the values saves for
+   * encoded are transformed to (value - 4).<br>
+   * When a chunk is ready (got 4 values), the {@link #encodeChunk()}
+   * takes control.
+   */
+  @Override
+  public void encode(int data) throws IOException {
+    if (data <= 3) {
+      indicator |= encodeTable[data][ordinal];
+    } else {
+      encodeQueue[encodeQueueSize++] = data - 4;
+    }
+    ++ordinal;
+
+    // If 4 values were encoded thus far, 'flush' them including the indicator.
+    if ((ordinal & 0x3) == 0) {
+      encodeChunk();
+    }
+  }
+
+  @Override
+  public IntDecoder createMatchingDecoder() {
+    return new FourFlagsIntDecoder();
+  }
+
+  @Override
+  public String toString() {
+    return "FourFlags (" + encoder.toString() + ")";
+  }
+
+}