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annotate dwt/internal/image/PngHuffmanTable.d @ 213:36f5cb12e1a2

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Update to SWT 3.4M7
author Frank Benoit <benoit@tionex.de>
date Sat, 17 May 2008 17:34:28 +0200
parents 57151e2793a2
children fd9c62a2998e
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1 /*******************************************************************************
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2 * Copyright (c) 2000, 2006 IBM Corporation and others.
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3 * All rights reserved. This program and the accompanying materials
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4 * are made available under the terms of the Eclipse Public License v1.0
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5 * which accompanies this distribution, and is available at
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6 * http://www.eclipse.org/legal/epl-v10.html
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7 *
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8 * Contributors:
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9 * IBM Corporation - initial API and implementation
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10 * Port to the D programming language:
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11 * Frank Benoit <benoit@tionex.de>
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12 *******************************************************************************/
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13 module dwt.internal.image.PngHuffmanTable;
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14
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15 import dwt.internal.image.PngDecodingDataStream;
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16
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17 public class PngHuffmanTable {
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18 CodeLengthInfo[] codeLengthInfo;
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19 int[] codeValues;
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20
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21 static const int MAX_CODE_LENGTH = 15;
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22 static const int BAD_CODE = 0xFFFFFFF;
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23 static const int incs[] = [1391376, 463792, 198768, 86961, 33936, 13776, 4592, 1968, 861, 336, 112, 48, 21, 7, 3, 1];
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24
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25 this (int[] lengths) {
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26 initialize(lengths);
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27 generateTable(lengths);
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28 }
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29
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30 private void initialize(int[] lengths) {
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31 codeValues = new int[lengths.length];
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32 for (int i = 0; i < codeValues.length; i++) {
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33 codeValues[i] = i;
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34 }
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35
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36 // minCodesByLength[n] : The smallest Huffman code of length n + 1.
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37 // maxCodesByLength[n] : The largest Huffman code of length n + 1.
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38 // indexesByLength[n] : Index into the values array. First value with a code of length n + 1.
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39 codeLengthInfo = new CodeLengthInfo[MAX_CODE_LENGTH];
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40 for (int i = 0; i < MAX_CODE_LENGTH; i++) {
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41 codeLengthInfo[i] = new CodeLengthInfo();
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42 codeLengthInfo[i].length = i;
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43 codeLengthInfo[i].baseIndex = 0;
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44 codeLengthInfo[i].min = BAD_CODE;
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45 codeLengthInfo[i].max = -1;
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46 }
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47 }
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48
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49 private void generateTable(int[] lengths) {
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50 // Sort the values using shellsort. Primary key is code size. Secondary key is value.
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51 int codeValuesTemp;
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52 for (int k = 0; k < 16; k++) {
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53 for (int h = incs[k], i = h; i < lengths.length; i++) {
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54 int v = lengths[i];
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55 codeValuesTemp = codeValues[i];
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56 int j = i;
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57 while (j >= h && (lengths[j - h] > v || (lengths[j - h] is v && codeValues[j - h] > codeValuesTemp))) {
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58 lengths[j] = lengths[j - h];
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59 codeValues[j] = codeValues[j - h];
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60 j -= h;
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61 }
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62 lengths[j] = v;
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63 codeValues[j] = codeValuesTemp;
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64 }
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65 }
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66
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67 // These values in these arrays correspond to the elements of the
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68 // "values" array. The Huffman code for codeValues[N] is codes[N]
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69 // and the length of the code is lengths[N].
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70 int[] codes = new int[lengths.length];
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71 int lastLength = 0;
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72 int code = 0;
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73 for (int i = 0; i < lengths.length; i++) {
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74 while (lastLength !is lengths[i]) {
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75 lastLength++;
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76 code <<= 1;
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77 }
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78 if (lastLength !is 0) {
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79 codes[i] = code;
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80 code++;
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81 }
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82 }
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83
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84 int last = 0;
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85 for (int i = 0; i < lengths.length; i++) {
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86 if (last !is lengths[i]) {
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87 last = lengths[i];
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88 codeLengthInfo[last - 1].baseIndex = i;
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89 codeLengthInfo[last - 1].min = codes[i];
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90 }
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91 if (last !is 0) codeLengthInfo[last - 1].max = codes[i];
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92 }
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93 }
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94
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95 int getNextValue(PngDecodingDataStream stream) {
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96 int code = stream.getNextIdatBit();
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97 int codelength = 0;
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98
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99 // Here we are taking advantage of the fact that 1 bits are used as
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100 // a prefix to the longer codeValues.
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101 while (codelength < MAX_CODE_LENGTH && code > codeLengthInfo[codelength].max) {
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102 code = ((code << 1) | stream.getNextIdatBit());
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103 codelength++;
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104 }
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105 if (codelength >= MAX_CODE_LENGTH) stream.error();
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106
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107 // Now we have a Huffman code of length (codelength + 1) that
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108 // is somewhere in the range
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109 // minCodesByLength[codelength]..maxCodesByLength[codelength].
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110 // This code is the (offset + 1)'th code of (codelength + 1);
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111 int offset = code - codeLengthInfo[codelength].min;
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112
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113 // indexesByLength[codelength] is the first code of length (codelength + 1)
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114 // so now we can look up the value for the Huffman code in the table.
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115 int index = codeLengthInfo[codelength].baseIndex + offset;
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116 return codeValues[index];
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117 }
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118
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119 static class CodeLengthInfo {
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120 int length;
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121 int max;
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122 int min;
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123 int baseIndex;
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124 }
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125
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126 }