1 7z Format description (2.30 Beta 25) |
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2 ----------------------------------- |
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3 |
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4 This file contains description of 7z archive format. |
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5 7z archive can contain files compressed with any method. |
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6 See "Methods.txt" for description for defined compressing methods. |
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7 |
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8 |
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9 Format structure Overview |
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10 ------------------------- |
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11 |
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12 Some fields can be optional. |
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13 |
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14 Archive structure |
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15 ~~~~~~~~~~~~~~~~~ |
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16 SignatureHeader |
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17 [PackedStreams] |
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18 [PackedStreamsForHeaders] |
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19 [ |
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20 Header |
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21 or |
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22 { |
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23 Packed Header |
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24 HeaderInfo |
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25 } |
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26 ] |
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27 |
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28 |
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29 |
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30 Header structure |
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31 ~~~~~~~~~~~~~~~~ |
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32 { |
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33 ArchiveProperties |
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34 AdditionalStreams |
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35 { |
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36 PackInfo |
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37 { |
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38 PackPos |
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39 NumPackStreams |
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40 Sizes[NumPackStreams] |
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41 CRCs[NumPackStreams] |
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42 } |
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43 CodersInfo |
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44 { |
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45 NumFolders |
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46 Folders[NumFolders] |
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47 { |
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48 NumCoders |
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49 CodersInfo[NumCoders] |
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50 { |
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51 ID |
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52 NumInStreams; |
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53 NumOutStreams; |
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54 PropertiesSize |
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55 Properties[PropertiesSize] |
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56 } |
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57 NumBindPairs |
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58 BindPairsInfo[NumBindPairs] |
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59 { |
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60 InIndex; |
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61 OutIndex; |
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62 } |
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63 PackedIndices |
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64 } |
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65 UnPackSize[Folders][Folders.NumOutstreams] |
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66 CRCs[NumFolders] |
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67 } |
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68 SubStreamsInfo |
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69 { |
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70 NumUnPackStreamsInFolders[NumFolders]; |
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71 UnPackSizes[] |
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72 CRCs[] |
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73 } |
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74 } |
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75 MainStreamsInfo |
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76 { |
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77 (Same as in AdditionalStreams) |
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78 } |
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79 FilesInfo |
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80 { |
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81 NumFiles |
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82 Properties[] |
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83 { |
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84 ID |
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85 Size |
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86 Data |
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87 } |
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88 } |
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89 } |
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90 |
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91 HeaderInfo structure |
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92 ~~~~~~~~~~~~~~~~~~~~ |
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93 { |
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94 (Same as in AdditionalStreams) |
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95 } |
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96 |
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97 |
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98 |
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99 Notes about Notation and encoding |
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100 --------------------------------- |
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101 |
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102 7z uses little endian encoding. |
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103 |
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104 7z archive format has optional headers that are marked as |
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105 [] |
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106 Header |
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107 [] |
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108 |
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109 REAL_UINT64 means real UINT64. |
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110 |
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111 UINT64 means real UINT64 encoded with the following scheme: |
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112 |
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113 Size of encoding sequence depends from first byte: |
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114 First_Byte Extra_Bytes Value |
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115 (binary) |
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116 0xxxxxxx : ( xxxxxxx ) |
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117 10xxxxxx BYTE y[1] : ( xxxxxx << (8 * 1)) + y |
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118 110xxxxx BYTE y[2] : ( xxxxx << (8 * 2)) + y |
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119 ... |
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120 1111110x BYTE y[6] : ( x << (8 * 6)) + y |
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121 11111110 BYTE y[7] : y |
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122 11111111 BYTE y[8] : y |
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123 |
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124 |
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125 |
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126 Property IDs |
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127 ------------ |
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128 |
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129 0x00 = kEnd, |
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130 |
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131 0x01 = kHeader, |
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132 |
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133 0x02 = kArchiveProperties, |
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134 |
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135 0x03 = kAdditionalStreamsInfo, |
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136 0x04 = kMainStreamsInfo, |
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137 0x05 = kFilesInfo, |
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138 |
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139 0x06 = kPackInfo, |
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140 0x07 = kUnPackInfo, |
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141 0x08 = kSubStreamsInfo, |
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142 |
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143 0x09 = kSize, |
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144 0x0A = kCRC, |
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145 |
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146 0x0B = kFolder, |
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147 |
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148 0x0C = kCodersUnPackSize, |
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149 0x0D = kNumUnPackStream, |
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150 |
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151 0x0E = kEmptyStream, |
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152 0x0F = kEmptyFile, |
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153 0x10 = kAnti, |
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154 |
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155 0x11 = kName, |
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156 0x12 = kCreationTime, |
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157 0x13 = kLastAccessTime, |
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158 0x14 = kLastWriteTime, |
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159 0x15 = kWinAttributes, |
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160 0x16 = kComment, |
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161 |
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162 0x17 = kEncodedHeader, |
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163 |
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164 |
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165 7z format headers |
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166 ----------------- |
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167 |
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168 SignatureHeader |
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169 ~~~~~~~~~~~~~~~ |
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170 BYTE kSignature[6] = {'7', 'z', 0xBC, 0xAF, 0x27, 0x1C}; |
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171 |
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172 ArchiveVersion |
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173 { |
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174 BYTE Major; // now = 0 |
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175 BYTE Minor; // now = 2 |
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176 }; |
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177 |
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178 UINT32 StartHeaderCRC; |
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179 |
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180 StartHeader |
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181 { |
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182 REAL_UINT64 NextHeaderOffset |
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183 REAL_UINT64 NextHeaderSize |
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184 UINT32 NextHeaderCRC |
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185 } |
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186 |
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187 |
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188 ........................... |
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189 |
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190 |
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191 ArchiveProperties |
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192 ~~~~~~~~~~~~~~~~~ |
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193 BYTE NID::kArchiveProperties (0x02) |
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194 for (;;) |
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195 { |
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196 BYTE PropertyType; |
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197 if (aType == 0) |
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198 break; |
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199 UINT64 PropertySize; |
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200 BYTE PropertyData[PropertySize]; |
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201 } |
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202 |
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203 |
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204 Digests (NumStreams) |
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205 ~~~~~~~~~~~~~~~~~~~~~ |
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206 BYTE AllAreDefined |
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207 if (AllAreDefined == 0) |
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208 { |
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209 for(NumStreams) |
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210 BIT Defined |
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211 } |
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212 UINT32 CRCs[NumDefined] |
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213 |
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214 |
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215 PackInfo |
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216 ~~~~~~~~~~~~ |
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217 BYTE NID::kPackInfo (0x06) |
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218 UINT64 PackPos |
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219 UINT64 NumPackStreams |
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220 |
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221 [] |
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222 BYTE NID::kSize (0x09) |
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223 UINT64 PackSizes[NumPackStreams] |
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224 [] |
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225 |
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226 [] |
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227 BYTE NID::kCRC (0x0A) |
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228 PackStreamDigests[NumPackStreams] |
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229 [] |
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230 |
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231 BYTE NID::kEnd |
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232 |
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233 |
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234 Folder |
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235 ~~~~~~ |
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236 UINT64 NumCoders; |
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237 for (NumCoders) |
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238 { |
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239 BYTE |
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240 { |
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241 0:3 DecompressionMethod.IDSize |
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242 4: |
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243 0 - IsSimple |
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244 1 - Is not simple |
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245 5: |
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246 0 - No Attributes |
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247 1 - There Are Attributes |
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248 7: |
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249 0 - Last Method in Alternative_Method_List |
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250 1 - There are more alternative methods |
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251 } |
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252 BYTE DecompressionMethod.ID[DecompressionMethod.IDSize] |
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253 if (!IsSimple) |
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254 { |
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255 UINT64 NumInStreams; |
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256 UINT64 NumOutStreams; |
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257 } |
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258 if (DecompressionMethod[0] != 0) |
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259 { |
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260 UINT64 PropertiesSize |
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261 BYTE Properties[PropertiesSize] |
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262 } |
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263 } |
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264 |
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265 NumBindPairs = NumOutStreamsTotal - 1; |
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266 |
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267 for (NumBindPairs) |
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268 { |
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269 UINT64 InIndex; |
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270 UINT64 OutIndex; |
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271 } |
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272 |
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273 NumPackedStreams = NumInStreamsTotal - NumBindPairs; |
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274 if (NumPackedStreams > 1) |
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275 for(NumPackedStreams) |
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276 { |
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277 UINT64 Index; |
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278 }; |
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279 |
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280 |
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281 |
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282 |
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283 Coders Info |
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284 ~~~~~~~~~~~ |
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285 |
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286 BYTE NID::kUnPackInfo (0x07) |
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287 |
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288 |
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289 BYTE NID::kFolder (0x0B) |
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290 UINT64 NumFolders |
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291 BYTE External |
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292 switch(External) |
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293 { |
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294 case 0: |
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295 Folders[NumFolders] |
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296 case 1: |
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297 UINT64 DataStreamIndex |
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298 } |
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299 |
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300 |
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301 BYTE ID::kCodersUnPackSize (0x0C) |
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302 for(Folders) |
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303 for(Folder.NumOutStreams) |
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304 UINT64 UnPackSize; |
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305 |
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306 |
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307 [] |
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308 BYTE NID::kCRC (0x0A) |
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309 UnPackDigests[NumFolders] |
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310 [] |
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311 |
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312 |
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313 |
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314 BYTE NID::kEnd |
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315 |
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316 |
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317 |
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318 SubStreams Info |
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319 ~~~~~~~~~~~~~~ |
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320 BYTE NID::kSubStreamsInfo; (0x08) |
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321 |
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322 [] |
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323 BYTE NID::kNumUnPackStream; (0x0D) |
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324 UINT64 NumUnPackStreamsInFolders[NumFolders]; |
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325 [] |
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326 |
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327 |
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328 [] |
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329 BYTE NID::kSize (0x09) |
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330 UINT64 UnPackSizes[] |
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331 [] |
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332 |
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333 |
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334 [] |
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335 BYTE NID::kCRC (0x0A) |
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336 Digests[Number of streams with unknown CRC] |
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337 [] |
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338 |
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339 |
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340 BYTE NID::kEnd |
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341 |
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342 |
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343 Streams Info |
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344 ~~~~~~~~~~~~ |
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345 |
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346 [] |
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347 PackInfo |
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348 [] |
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349 |
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350 |
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351 [] |
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352 CodersInfo |
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353 [] |
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354 |
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355 |
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356 [] |
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357 SubStreamsInfo |
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358 [] |
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359 |
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360 BYTE NID::kEnd |
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361 |
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362 |
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363 FilesInfo |
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364 ~~~~~~~~~ |
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365 BYTE NID::kFilesInfo; (0x05) |
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366 UINT64 NumFiles |
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367 |
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368 for (;;) |
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369 { |
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370 BYTE PropertyType; |
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371 if (aType == 0) |
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372 break; |
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373 |
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374 UINT64 Size; |
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375 |
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376 switch(PropertyType) |
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377 { |
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378 kEmptyStream: (0x0E) |
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379 for(NumFiles) |
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380 BIT IsEmptyStream |
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381 |
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382 kEmptyFile: (0x0F) |
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383 for(EmptyStreams) |
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384 BIT IsEmptyFile |
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385 |
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386 kAnti: (0x10) |
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387 for(EmptyStreams) |
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388 BIT IsAntiFile |
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389 |
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390 case kCreationTime: (0x12) |
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391 case kLastAccessTime: (0x13) |
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392 case kLastWriteTime: (0x14) |
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393 BYTE AllAreDefined |
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394 if (AllAreDefined == 0) |
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395 { |
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396 for(NumFiles) |
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397 BIT TimeDefined |
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398 } |
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399 BYTE External; |
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400 if(External != 0) |
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401 UINT64 DataIndex |
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402 [] |
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403 for(Definded Items) |
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404 UINT32 Time |
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405 [] |
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406 |
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407 kNames: (0x11) |
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408 BYTE External; |
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409 if(External != 0) |
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410 UINT64 DataIndex |
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411 [] |
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412 for(Files) |
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413 { |
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414 wchar_t Names[NameSize]; |
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415 wchar_t 0; |
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416 } |
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417 [] |
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418 |
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419 kAttributes: (0x15) |
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420 BYTE AllAreDefined |
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421 if (AllAreDefined == 0) |
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422 { |
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423 for(NumFiles) |
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424 BIT AttributesAreDefined |
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425 } |
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426 BYTE External; |
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427 if(External != 0) |
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428 UINT64 DataIndex |
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429 [] |
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430 for(Definded Attributes) |
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431 UINT32 Attributes |
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432 [] |
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433 } |
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434 } |
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435 |
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436 |
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437 Header |
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438 ~~~~~~ |
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439 BYTE NID::kHeader (0x01) |
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440 |
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441 [] |
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442 ArchiveProperties |
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443 [] |
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444 |
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445 [] |
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446 BYTE NID::kAdditionalStreamsInfo; (0x03) |
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447 StreamsInfo |
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448 [] |
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449 |
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450 [] |
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451 BYTE NID::kMainStreamsInfo; (0x04) |
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452 StreamsInfo |
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453 [] |
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454 |
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455 [] |
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456 FilesInfo |
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457 [] |
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458 |
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459 BYTE NID::kEnd |
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460 |
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461 |
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462 HeaderInfo |
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463 ~~~~~~~~~~ |
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464 [] |
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465 BYTE NID::kEncodedHeader; (0x17) |
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466 StreamsInfo for Encoded Header |
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467 [] |
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468 |
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469 |
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470 --- |
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471 End of document |
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