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188 lines
5.2 KiB
Plaintext
188 lines
5.2 KiB
Plaintext
7z ANSI-C Decoder 9.35
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----------------------
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7z ANSI-C provides 7z/LZMA decoding.
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7z ANSI-C version is simplified version ported from C++ code.
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LZMA is default and general compression method of 7z format
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in 7-Zip compression program (www.7-zip.org). LZMA provides high
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compression ratio and very fast decompression.
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LICENSE
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-------
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7z ANSI-C Decoder is part of the LZMA SDK.
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LZMA SDK is written and placed in the public domain by Igor Pavlov.
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Files
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---------------------
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7zDecode.* - Low level 7z decoding
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7zExtract.* - High level 7z decoding
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7zHeader.* - .7z format constants
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7zIn.* - .7z archive opening
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7zItem.* - .7z structures
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7zMain.c - Test application
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How To Use
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----------
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You can create .7z archive with 7z.exe, 7za.exe or 7zr.exe:
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7z.exe a archive.7z *.htm -r -mx -m0fb=255
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If you have big number of files in archive, and you need fast extracting,
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you can use partly-solid archives:
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7za.exe a archive.7z *.htm -ms=512K -r -mx -m0fb=255 -m0d=512K
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In that example 7-Zip will use 512KB solid blocks. So it needs to decompress only
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512KB for extracting one file from such archive.
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Limitations of current version of 7z ANSI-C Decoder
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---------------------------------------------------
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- It reads only "FileName", "Size", "LastWriteTime" and "CRC" information for each file in archive.
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- It supports only LZMA and Copy (no compression) methods with BCJ or BCJ2 filters.
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- It converts original UTF-16 Unicode file names to UTF-8 Unicode file names.
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These limitations will be fixed in future versions.
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Using 7z ANSI-C Decoder Test application:
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-----------------------------------------
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Usage: 7zDec <command> <archive_name>
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<Command>:
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e: Extract files from archive
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l: List contents of archive
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t: Test integrity of archive
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Example:
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7zDec l archive.7z
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lists contents of archive.7z
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7zDec e archive.7z
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extracts files from archive.7z to current folder.
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How to use .7z Decoder
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----------------------
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Memory allocation
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~~~~~~~~~~~~~~~~~
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7z Decoder uses two memory pools:
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1) Temporary pool
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2) Main pool
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Such scheme can allow you to avoid fragmentation of allocated blocks.
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Steps for using 7z decoder
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--------------------------
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Use code at 7zMain.c as example.
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1) Declare variables:
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inStream /* implements ILookInStream interface */
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CSzArEx db; /* 7z archive database structure */
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ISzAlloc allocImp; /* memory functions for main pool */
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ISzAlloc allocTempImp; /* memory functions for temporary pool */
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2) call CrcGenerateTable(); function to initialize CRC structures.
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3) call SzArEx_Init(&db); function to initialize db structures.
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4) call SzArEx_Open(&db, inStream, &allocMain, &allocTemp) to open archive
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This function opens archive "inStream" and reads headers to "db".
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All items in "db" will be allocated with "allocMain" functions.
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SzArEx_Open function allocates and frees temporary structures by "allocTemp" functions.
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5) List items or Extract items
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Listing code:
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~~~~~~~~~~~~~
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Use SzArEx_GetFileNameUtf16 function. Look example code in C\Util\7z\7zMain.c file.
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Extracting code:
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~~~~~~~~~~~~~~~~
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SZ_RESULT SzAr_Extract(
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CArchiveDatabaseEx *db,
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ILookInStream *inStream,
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UInt32 fileIndex, /* index of file */
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UInt32 *blockIndex, /* index of solid block */
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Byte **outBuffer, /* pointer to pointer to output buffer (allocated with allocMain) */
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size_t *outBufferSize, /* buffer size for output buffer */
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size_t *offset, /* offset of stream for required file in *outBuffer */
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size_t *outSizeProcessed, /* size of file in *outBuffer */
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ISzAlloc *allocMain,
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ISzAlloc *allocTemp);
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If you need to decompress more than one file, you can send these values from previous call:
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blockIndex,
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outBuffer,
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outBufferSize,
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You can consider "outBuffer" as cache of solid block. If your archive is solid,
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it will increase decompression speed.
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After decompressing you must free "outBuffer":
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allocImp.Free(outBuffer);
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6) call SzArEx_Free(&db, allocImp.Free) to free allocated items in "db".
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Memory requirements for .7z decoding
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------------------------------------
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Memory usage for Archive opening:
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- Temporary pool:
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- Memory for uncompressed .7z headers
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- some other temporary blocks
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- Main pool:
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- Memory for database:
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Estimated size of one file structures in solid archive:
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- Size (4 or 8 Bytes)
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- CRC32 (4 bytes)
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- LastWriteTime (8 bytes)
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- Some file information (4 bytes)
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- File Name (variable length) + pointer + allocation structures
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Memory usage for archive Decompressing:
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- Temporary pool:
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- Memory for LZMA decompressing structures
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- Main pool:
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- Memory for decompressed solid block
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- Memory for temprorary buffers, if BCJ2 fileter is used. Usually these
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temprorary buffers can be about 15% of solid block size.
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7z Decoder doesn't allocate memory for compressed blocks.
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Instead of this, you must allocate buffer with desired
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size before calling 7z Decoder. Use 7zMain.c as example.
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Defines
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-------
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_SZ_ALLOC_DEBUG - define it if you want to debug alloc/free operations to stderr.
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---
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http://www.7-zip.org
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http://www.7-zip.org/sdk.html
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http://www.7-zip.org/support.html
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