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 * https://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 * A 256 entry Move To Front transform.
20 */
21 final class Bzip2MoveToFrontTable {
22 /**
23 * The Move To Front list.
24 */
25 private final byte[] mtf = {
26 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
27 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
28 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
29 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
30 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
31 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95,
32 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111,
33 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127,
34 (byte) 128, (byte) 129, (byte) 130, (byte) 131, (byte) 132, (byte) 133, (byte) 134, (byte) 135,
35 (byte) 136, (byte) 137, (byte) 138, (byte) 139, (byte) 140, (byte) 141, (byte) 142, (byte) 143,
36 (byte) 144, (byte) 145, (byte) 146, (byte) 147, (byte) 148, (byte) 149, (byte) 150, (byte) 151,
37 (byte) 152, (byte) 153, (byte) 154, (byte) 155, (byte) 156, (byte) 157, (byte) 158, (byte) 159,
38 (byte) 160, (byte) 161, (byte) 162, (byte) 163, (byte) 164, (byte) 165, (byte) 166, (byte) 167,
39 (byte) 168, (byte) 169, (byte) 170, (byte) 171, (byte) 172, (byte) 173, (byte) 174, (byte) 175,
40 (byte) 176, (byte) 177, (byte) 178, (byte) 179, (byte) 180, (byte) 181, (byte) 182, (byte) 183,
41 (byte) 184, (byte) 185, (byte) 186, (byte) 187, (byte) 188, (byte) 189, (byte) 190, (byte) 191,
42 (byte) 192, (byte) 193, (byte) 194, (byte) 195, (byte) 196, (byte) 197, (byte) 198, (byte) 199,
43 (byte) 200, (byte) 201, (byte) 202, (byte) 203, (byte) 204, (byte) 205, (byte) 206, (byte) 207,
44 (byte) 208, (byte) 209, (byte) 210, (byte) 211, (byte) 212, (byte) 213, (byte) 214, (byte) 215,
45 (byte) 216, (byte) 217, (byte) 218, (byte) 219, (byte) 220, (byte) 221, (byte) 222, (byte) 223,
46 (byte) 224, (byte) 225, (byte) 226, (byte) 227, (byte) 228, (byte) 229, (byte) 230, (byte) 231,
47 (byte) 232, (byte) 233, (byte) 234, (byte) 235, (byte) 236, (byte) 237, (byte) 238, (byte) 239,
48 (byte) 240, (byte) 241, (byte) 242, (byte) 243, (byte) 244, (byte) 245, (byte) 246, (byte) 247,
49 (byte) 248, (byte) 249, (byte) 250, (byte) 251, (byte) 252, (byte) 253, (byte) 254, (byte) 255
50 };
51
52 /**
53 * Moves a value to the head of the MTF list (forward Move To Front transform).
54 * @param value The value to move
55 * @return The position the value moved from
56 */
57 int valueToFront(final byte value) {
58 int index = 0;
59 byte temp = mtf[0];
60 if (value != temp) {
61 mtf[0] = value;
62 while (value != temp) {
63 index++;
64 final byte temp2 = temp;
65 temp = mtf[index];
66 mtf[index] = temp2;
67 }
68 }
69 return index;
70 }
71
72 /**
73 * Gets the value from a given index and moves it to the front of the MTF list (inverse Move To Front transform).
74 * @param index The index to move
75 * @return The value at the given index
76 */
77 byte indexToFront(final int index) {
78 final byte value = mtf[index];
79 System.arraycopy(mtf, 0, mtf, 1, index);
80 mtf[0] = value;
81
82 return value;
83 }
84 }
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