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comparison dwt/internal/image/PngHuffmanTable.d @ 0:380af2bdd8e5

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author Jacob Carlborg <doob@me.com> <jacob.carlborg@gmail.com>
date Sat, 09 Aug 2008 17:00:02 +0200
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1 /*******************************************************************************
2 * Copyright (c) 2000, 2006 IBM Corporation and others.
3 * All rights reserved. This program and the accompanying materials
4 * are made available under the terms of the Eclipse Public License v1.0
5 * which accompanies this distribution, and is available at
6 * http://www.eclipse.org/legal/epl-v10.html
7 *
8 * Contributors:
9 * IBM Corporation - initial API and implementation
10 *******************************************************************************/
11 module dwt.internal.image;
12
13 import java.io.IOException;
14
15 public class PngHuffmanTable {
16 CodeLengthInfo[] codeLengthInfo;
17 int[] codeValues;
18
19 static final int MAX_CODE_LENGTH = 15;
20 static final int BAD_CODE = 0xFFFFFFF;
21 static final int incs[] = {1391376, 463792, 198768, 86961, 33936, 13776, 4592, 1968, 861, 336, 112, 48, 21, 7, 3, 1};
22
23 PngHuffmanTable (int[] lengths) {
24 super();
25 initialize(lengths);
26 generateTable(lengths);
27 }
28
29 private void initialize(int[] lengths) {
30 codeValues = new int[lengths.length];
31 for (int i = 0; i < codeValues.length; i++) {
32 codeValues[i] = i;
33 }
34
35 // minCodesByLength[n] : The smallest Huffman code of length n + 1.
36 // maxCodesByLength[n] : The largest Huffman code of length n + 1.
37 // indexesByLength[n] : Index into the values array. First value with a code of length n + 1.
38 codeLengthInfo = new CodeLengthInfo[MAX_CODE_LENGTH];
39 for (int i = 0; i < MAX_CODE_LENGTH; i++) {
40 codeLengthInfo[i] = new CodeLengthInfo();
41 codeLengthInfo[i].length = i;
42 codeLengthInfo[i].baseIndex = 0;
43 codeLengthInfo[i].min = BAD_CODE;
44 codeLengthInfo[i].max = -1;
45 }
46 }
47
48 private void generateTable(int[] lengths) {
49 // Sort the values using shellsort. Primary key is code size. Secondary key is value.
50 int codeValuesTemp;
51 for (int k = 0; k < 16; k++) {
52 for (int h = incs[k], i = h; i < lengths.length; i++) {
53 int v = lengths[i];
54 codeValuesTemp = codeValues[i];
55 int j = i;
56 while (j >= h && (lengths[j - h] > v || (lengths[j - h] is v && codeValues[j - h] > codeValuesTemp))) {
57 lengths[j] = lengths[j - h];
58 codeValues[j] = codeValues[j - h];
59 j -= h;
60 }
61 lengths[j] = v;
62 codeValues[j] = codeValuesTemp;
63 }
64 }
65
66 // These values in these arrays correspond to the elements of the
67 // "values" array. The Huffman code for codeValues[N] is codes[N]
68 // and the length of the code is lengths[N].
69 int[] codes = new int[lengths.length];
70 int lastLength = 0;
71 int code = 0;
72 for (int i = 0; i < lengths.length; i++) {
73 while (lastLength !is lengths[i]) {
74 lastLength++;
75 code <<= 1;
76 }
77 if (lastLength !is 0) {
78 codes[i] = code;
79 code++;
80 }
81 }
82
83 int last = 0;
84 for (int i = 0; i < lengths.length; i++) {
85 if (last !is lengths[i]) {
86 last = lengths[i];
87 codeLengthInfo[last - 1].baseIndex = i;
88 codeLengthInfo[last - 1].min = codes[i];
89 }
90 if (last !is 0) codeLengthInfo[last - 1].max = codes[i];
91 }
92 }
93
94 int getNextValue(PngDecodingDataStream stream) throws IOException {
95 int code = stream.getNextIdatBit();
96 int codelength = 0;
97
98 // Here we are taking advantage of the fact that 1 bits are used as
99 // a prefix to the longer codeValues.
100 while (codelength < MAX_CODE_LENGTH && code > codeLengthInfo[codelength].max) {
101 code = ((code << 1) | stream.getNextIdatBit());
102 codelength++;
103 }
104 if (codelength >= MAX_CODE_LENGTH) stream.error();
105
106 // Now we have a Huffman code of length (codelength + 1) that
107 // is somewhere in the range
108 // minCodesByLength[codelength]..maxCodesByLength[codelength].
109 // This code is the (offset + 1)'th code of (codelength + 1);
110 int offset = code - codeLengthInfo[codelength].min;
111
112 // indexesByLength[codelength] is the first code of length (codelength + 1)
113 // so now we can look up the value for the Huffman code in the table.
114 int index = codeLengthInfo[codelength].baseIndex + offset;
115 return codeValues[index];
116 }
117
118 static class CodeLengthInfo {
119 int length;
120 int max;
121 int min;
122 int baseIndex;
123 }
124
125 }