pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / contrib / facet / src / java / org / apache / lucene / util / encoding / VInt8IntEncoder.java

diff --git a/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/VInt8IntEncoder.java b/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/VInt8IntEncoder.java
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+++ b/lucene-java-3.5.0/lucene/contrib/facet/src/java/org/apache/lucene/util/encoding/VInt8IntEncoder.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.
+ */
+
+/**
+ * An {@link IntEncoder} which implements variable length encoding. A number is
+ * encoded as follows:
+ * <ul>
+ * <li>If it is less than 127 and non-negative, i.e. uses only 7 bits, it is
+ * encoded as a single byte: 0bbbbbbb.
+ * <li>If it occupies more than 7 bits, it is represented as a series of bytes,
+ * each byte carrying 7 bits. All but the last byte have the MSB set, the last
+ * one has it unset.
+ * </ul>
+ * Example:
+ * <ol>
+ * <li>n = 117 = 01110101: This has less than 8 significant bits, therefore is
+ * encoded as 01110101 = 0x75.
+ * <li>n = 100000 = (binary) 11000011010100000. This has 17 significant bits,
+ * thus needs three Vint8 bytes. Pad it to a multiple of 7 bits, then split it
+ * into chunks of 7 and add an MSB, 0 for the last byte, 1 for the others:
+ * 1|0000110 1|0001101 0|0100000 = 0x86 0x8D 0x20.
+ * </ol>
+ * <b>NOTE:</b> although this encoder is not limited to values &ge; 0, it is not
+ * recommended for use with negative values, as their encoding will result in 5
+ * bytes written to the output stream, rather than 4. For such values, either
+ * use {@link SimpleIntEncoder} or write your own version of variable length
+ * encoding, which can better handle negative values.
+ * 
+ * @lucene.experimental
+ */
+public class VInt8IntEncoder extends IntEncoder {
+
+  @Override
+  public void encode(int value) throws IOException {
+    if ((value & ~0x7F) == 0) {
+      out.write(value);
+    } else if ((value & ~0x3FFF) == 0) {
+      out.write(0x80 | (value >> 7));
+      out.write(0x7F & value);
+    } else if ((value & ~0x1FFFFF) == 0) {
+      out.write(0x80 | (value >> 14));
+      out.write(0x80 | (value >> 7));
+      out.write(0x7F & value);
+    } else if ((value & ~0xFFFFFFF) == 0) {
+      out.write(0x80 | (value >> 21));
+      out.write(0x80 | (value >> 14));
+      out.write(0x80 | (value >> 7));
+      out.write(0x7F & value);
+    } else {
+      out.write(0x80 | (value >> 28));
+      out.write(0x80 | (value >> 21));
+      out.write(0x80 | (value >> 14));
+      out.write(0x80 | (value >> 7));
+      out.write(0x7F & value);
+    }
+  }
+
+  @Override
+  public IntDecoder createMatchingDecoder() {
+    return new VInt8IntDecoder();
+  }
+
+  @Override
+  public String toString() {
+    return "VInt8";
+  }
+
+}