1 | 7z ANSI-C Decoder 4.62
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2 | ----------------------
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3 |
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4 | 7z ANSI-C provides 7z/LZMA decoding.
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5 | 7z ANSI-C version is simplified version ported from C++ code.
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6 |
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7 | LZMA is default and general compression method of 7z format
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8 | in 7-Zip compression program (www.7-zip.org). LZMA provides high
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9 | compression ratio and very fast decompression.
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10 |
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11 |
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12 | LICENSE
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13 | -------
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14 |
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15 | 7z ANSI-C Decoder is part of the LZMA SDK.
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16 | LZMA SDK is written and placed in the public domain by Igor Pavlov.
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17 |
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18 | Files
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19 | ---------------------
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20 |
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21 | 7zDecode.* - Low level 7z decoding
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22 | 7zExtract.* - High level 7z decoding
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23 | 7zHeader.* - .7z format constants
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24 | 7zIn.* - .7z archive opening
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25 | 7zItem.* - .7z structures
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26 | 7zMain.c - Test application
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27 |
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28 |
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29 | How To Use
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30 | ----------
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31 |
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32 | You must download 7-Zip program from www.7-zip.org.
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33 |
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34 | You can create .7z archive with 7z.exe or 7za.exe:
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35 |
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36 | 7za.exe a archive.7z *.htm -r -mx -m0fb=255
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37 |
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38 | If you have big number of files in archive, and you need fast extracting,
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39 | you can use partly-solid archives:
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40 |
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41 | 7za.exe a archive.7z *.htm -ms=512K -r -mx -m0fb=255 -m0d=512K
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42 |
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43 | In that example 7-Zip will use 512KB solid blocks. So it needs to decompress only
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44 | 512KB for extracting one file from such archive.
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45 |
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46 |
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47 | Limitations of current version of 7z ANSI-C Decoder
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48 | ---------------------------------------------------
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49 |
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50 | - It reads only "FileName", "Size", "LastWriteTime" and "CRC" information for each file in archive.
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51 | - It supports only LZMA and Copy (no compression) methods with BCJ or BCJ2 filters.
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52 | - It converts original UTF-16 Unicode file names to UTF-8 Unicode file names.
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53 |
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54 | These limitations will be fixed in future versions.
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55 |
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56 |
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57 | Using 7z ANSI-C Decoder Test application:
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58 | -----------------------------------------
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59 |
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60 | Usage: 7zDec <command> <archive_name>
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61 |
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62 | <Command>:
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63 | e: Extract files from archive
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64 | l: List contents of archive
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65 | t: Test integrity of archive
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66 |
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67 | Example:
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68 |
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69 | 7zDec l archive.7z
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70 |
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71 | lists contents of archive.7z
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72 |
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73 | 7zDec e archive.7z
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74 |
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75 | extracts files from archive.7z to current folder.
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76 |
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77 |
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78 | How to use .7z Decoder
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79 | ----------------------
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80 |
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81 | Memory allocation
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82 | ~~~~~~~~~~~~~~~~~
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83 |
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84 | 7z Decoder uses two memory pools:
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85 | 1) Temporary pool
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86 | 2) Main pool
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87 | Such scheme can allow you to avoid fragmentation of allocated blocks.
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88 |
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89 |
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90 | Steps for using 7z decoder
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91 | --------------------------
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92 |
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93 | Use code at 7zMain.c as example.
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94 |
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95 | 1) Declare variables:
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96 | inStream /* implements ILookInStream interface */
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97 | CSzArEx db; /* 7z archive database structure */
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98 | ISzAlloc allocImp; /* memory functions for main pool */
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99 | ISzAlloc allocTempImp; /* memory functions for temporary pool */
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100 |
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101 | 2) call CrcGenerateTable(); function to initialize CRC structures.
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102 |
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103 | 3) call SzArEx_Init(&db); function to initialize db structures.
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104 |
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105 | 4) call SzArEx_Open(&db, inStream, &allocMain, &allocTemp) to open archive
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106 |
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107 | This function opens archive "inStream" and reads headers to "db".
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108 | All items in "db" will be allocated with "allocMain" functions.
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109 | SzArEx_Open function allocates and frees temporary structures by "allocTemp" functions.
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110 |
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111 | 5) List items or Extract items
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112 |
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113 | Listing code:
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114 | ~~~~~~~~~~~~~
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115 | {
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116 | UInt32 i;
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117 | for (i = 0; i < db.db.NumFiles; i++)
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118 | {
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119 | CFileItem *f = db.db.Files + i;
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120 | printf("%10d %s\n", (int)f->Size, f->Name);
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121 | }
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122 | }
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123 |
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124 | Extracting code:
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125 | ~~~~~~~~~~~~~~~~
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126 |
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127 | SZ_RESULT SzAr_Extract(
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128 | CArchiveDatabaseEx *db,
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129 | ILookInStream *inStream,
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130 | UInt32 fileIndex, /* index of file */
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131 | UInt32 *blockIndex, /* index of solid block */
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132 | Byte **outBuffer, /* pointer to pointer to output buffer (allocated with allocMain) */
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133 | size_t *outBufferSize, /* buffer size for output buffer */
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134 | size_t *offset, /* offset of stream for required file in *outBuffer */
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135 | size_t *outSizeProcessed, /* size of file in *outBuffer */
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136 | ISzAlloc *allocMain,
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137 | ISzAlloc *allocTemp);
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138 |
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139 | If you need to decompress more than one file, you can send these values from previous call:
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140 | blockIndex,
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141 | outBuffer,
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142 | outBufferSize,
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143 | You can consider "outBuffer" as cache of solid block. If your archive is solid,
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144 | it will increase decompression speed.
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145 |
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146 | After decompressing you must free "outBuffer":
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147 | allocImp.Free(outBuffer);
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148 |
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149 | 6) call SzArEx_Free(&db, allocImp.Free) to free allocated items in "db".
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150 |
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151 |
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152 |
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153 |
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154 | Memory requirements for .7z decoding
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155 | ------------------------------------
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156 |
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157 | Memory usage for Archive opening:
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158 | - Temporary pool:
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159 | - Memory for uncompressed .7z headers
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160 | - some other temporary blocks
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161 | - Main pool:
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162 | - Memory for database:
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163 | Estimated size of one file structures in solid archive:
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164 | - Size (4 or 8 Bytes)
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165 | - CRC32 (4 bytes)
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166 | - LastWriteTime (8 bytes)
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167 | - Some file information (4 bytes)
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168 | - File Name (variable length) + pointer + allocation structures
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169 |
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170 | Memory usage for archive Decompressing:
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171 | - Temporary pool:
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172 | - Memory for LZMA decompressing structures
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173 | - Main pool:
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174 | - Memory for decompressed solid block
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175 | - Memory for temprorary buffers, if BCJ2 fileter is used. Usually these
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176 | temprorary buffers can be about 15% of solid block size.
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177 |
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178 |
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179 | 7z Decoder doesn't allocate memory for compressed blocks.
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180 | Instead of this, you must allocate buffer with desired
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181 | size before calling 7z Decoder. Use 7zMain.c as example.
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182 |
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183 |
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184 | Defines
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185 | -------
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186 |
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187 | _SZ_ALLOC_DEBUG - define it if you want to debug alloc/free operations to stderr.
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188 |
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189 |
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190 | ---
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191 |
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192 | http://www.7-zip.org
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193 | http://www.7-zip.org/sdk.html
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194 | http://www.7-zip.org/support.html
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