1 /*
2 * Copyright 2014 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License,
5 * version 2.0 (the "License"); you may not use this file except in compliance
6 * with the License. You may obtain a copy of the License at:
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16 package io.netty.handler.codec.compression;
17
18 /**
19 * Constants for both the {@link Bzip2Encoder} and the {@link Bzip2Decoder}.
20 */
21 final class Bzip2Constants {
22
23 /**
24 * Magic number of Bzip2 stream.
25 */
26 static final int MAGIC_NUMBER = 'B' << 16 | 'Z' << 8 | 'h';
27
28 /**
29 * Block header magic number. Equals to BCD (pi).
30 */
31 static final int BLOCK_HEADER_MAGIC_1 = 0x314159;
32 static final int BLOCK_HEADER_MAGIC_2 = 0x265359;
33
34 /**
35 * End of stream magic number. Equals to BCD sqrt(pi).
36 */
37 static final int END_OF_STREAM_MAGIC_1 = 0x177245;
38 static final int END_OF_STREAM_MAGIC_2 = 0x385090;
39
40 /**
41 * Base block size.
42 */
43 static final int BASE_BLOCK_SIZE = 100000;
44
45 /**
46 * Minimum and maximum size of one block.
47 * Must be multiplied by {@link Bzip2Constants#BASE_BLOCK_SIZE}.
48 */
49 static final int MIN_BLOCK_SIZE = 1;
50 static final int MAX_BLOCK_SIZE = 9;
51
52 /**
53 * Maximum possible Huffman alphabet size.
54 */
55 static final int HUFFMAN_MAX_ALPHABET_SIZE = 258;
56
57 /**
58 * The longest Huffman code length created by the encoder.
59 */
60 static final int HUFFMAN_ENCODE_MAX_CODE_LENGTH = 20;
61
62 /**
63 * The longest Huffman code length accepted by the decoder.
64 */
65 static final int HUFFMAN_DECODE_MAX_CODE_LENGTH = 23;
66
67 /**
68 * Huffman symbols used for run-length encoding.
69 */
70 static final int HUFFMAN_SYMBOL_RUNA = 0;
71 static final int HUFFMAN_SYMBOL_RUNB = 1;
72
73 /**
74 * Huffman symbols range size for Huffman used map.
75 */
76 static final int HUFFMAN_SYMBOL_RANGE_SIZE = 16;
77
78 /**
79 * Maximum length of zero-terminated bit runs of MTF'ed Huffman table.
80 */
81 static final int HUFFMAN_SELECTOR_LIST_MAX_LENGTH = 6;
82
83 /**
84 * Number of symbols decoded after which a new Huffman table is selected.
85 */
86 static final int HUFFMAN_GROUP_RUN_LENGTH = 50;
87
88 /**
89 * Maximum possible number of Huffman table selectors.
90 */
91 static final int MAX_SELECTORS = 2 + 900000 / HUFFMAN_GROUP_RUN_LENGTH; // 18002
92
93 /**
94 * Minimum number of alternative Huffman tables.
95 */
96 static final int HUFFMAN_MINIMUM_TABLES = 2;
97
98 /**
99 * Maximum number of alternative Huffman tables.
100 */
101 static final int HUFFMAN_MAXIMUM_TABLES = 6;
102
103 private Bzip2Constants() { }
104 }