pylucene 3.5.0-3

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

diff --git a/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/EightFlagsIntEncoder.java b/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/EightFlagsIntEncoder.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 data in chunks of 8. Every group starts with a single
+ * byte (called indicator) which represents 8 - 1 bit flags, where the value:
+ * <ul>
+ * <li>1 means the encoded value is '1'
+ * <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 is encoded in the indicator, the actual
+ * value that is encoded is <code>value-2</code>, which saves some more bits.
+ * </ul>
+ * Encoding example:
+ * <ul>
+ * <li>Original values: 6, 16, 5, 9, 7, 1
+ * <li>After sorting: 1, 5, 6, 7, 9, 16
+ * <li>D-Gap computing: 1, 4, 1, 1, 2, 5 (so far - done by
+ * {@link DGapIntEncoder})
+ * <li>Encoding: 1,0,1,1,0,0,0,0 as the indicator, by 2 (4-2), 0 (2-2), 3 (5-2).
+ * <li>Binary encode: <u>0 | 0 | 0 | 0 | 1 | 1 | 0 | 1</u> 00000010 00000000
+ * 00000011 (indicator is <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 EightFlagsIntEncoder extends ChunksIntEncoder {
+
+  /**
+   * Holds all combinations of <i>indicator</i> flags for fast encoding (saves
+   * time on bit manipulation at encode time)
+   */
+  private static byte[] encodeTable = new byte[] { 0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, (byte) 0x80 };
+
+  public EightFlagsIntEncoder() {
+    super(8);
+  }
+
+  @Override
+  public void encode(int data) throws IOException {
+    if (data == 1) {
+      indicator |= encodeTable[ordinal];
+    } else {
+      encodeQueue[encodeQueueSize++] = data - 2;
+    }
+    ++ordinal;
+
+    // If 8 values were encoded thus far, 'flush' them including the indicator.
+    if ((ordinal & 0x7) == 0) {
+      encodeChunk();
+    }
+  }
+
+  @Override
+  public IntDecoder createMatchingDecoder() {
+    return new EightFlagsIntDecoder();
+  }
+
+  @Override
+  public String toString() {
+    return "EightFlags (" + encoder.toString() + ")";
+  }
+
+}