1 package org.apache.lucene.util.encoding;
3 import java.io.IOException;
6 * Licensed to the Apache Software Foundation (ASF) under one or more
7 * contributor license agreements. See the NOTICE file distributed with
8 * this work for additional information regarding copyright ownership.
9 * The ASF licenses this file to You under the Apache License, Version 2.0
10 * (the "License"); you may not use this file except in compliance with
11 * the License. You may obtain a copy of the License at
13 * http://www.apache.org/licenses/LICENSE-2.0
15 * Unless required by applicable law or agreed to in writing, software
16 * distributed under the License is distributed on an "AS IS" BASIS,
17 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
18 * See the License for the specific language governing permissions and
19 * limitations under the License.
23 * An {@link IntEncoder} which implements variable length encoding. A number is
26 * <li>If it is less than 127 and non-negative, i.e. uses only 7 bits, it is
27 * encoded as a single byte: 0bbbbbbb.
28 * <li>If it occupies more than 7 bits, it is represented as a series of bytes,
29 * each byte carrying 7 bits. All but the last byte have the MSB set, the last
34 * <li>n = 117 = 01110101: This has less than 8 significant bits, therefore is
35 * encoded as 01110101 = 0x75.
36 * <li>n = 100000 = (binary) 11000011010100000. This has 17 significant bits,
37 * thus needs three Vint8 bytes. Pad it to a multiple of 7 bits, then split it
38 * into chunks of 7 and add an MSB, 0 for the last byte, 1 for the others:
39 * 1|0000110 1|0001101 0|0100000 = 0x86 0x8D 0x20.
41 * <b>NOTE:</b> although this encoder is not limited to values ≥ 0, it is not
42 * recommended for use with negative values, as their encoding will result in 5
43 * bytes written to the output stream, rather than 4. For such values, either
44 * use {@link SimpleIntEncoder} or write your own version of variable length
45 * encoding, which can better handle negative values.
47 * @lucene.experimental
49 public class VInt8IntEncoder extends IntEncoder {
52 public void encode(int value) throws IOException {
53 if ((value & ~0x7F) == 0) {
55 } else if ((value & ~0x3FFF) == 0) {
56 out.write(0x80 | (value >> 7));
57 out.write(0x7F & value);
58 } else if ((value & ~0x1FFFFF) == 0) {
59 out.write(0x80 | (value >> 14));
60 out.write(0x80 | (value >> 7));
61 out.write(0x7F & value);
62 } else if ((value & ~0xFFFFFFF) == 0) {
63 out.write(0x80 | (value >> 21));
64 out.write(0x80 | (value >> 14));
65 out.write(0x80 | (value >> 7));
66 out.write(0x7F & value);
68 out.write(0x80 | (value >> 28));
69 out.write(0x80 | (value >> 21));
70 out.write(0x80 | (value >> 14));
71 out.write(0x80 | (value >> 7));
72 out.write(0x7F & value);
77 public IntDecoder createMatchingDecoder() {
78 return new VInt8IntDecoder();
82 public String toString() {