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4.20
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Igor Pavlov
committed by
Kornel Lesiński
Kornel Lesiński
parent
8c1b5c7b7e
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238
DOC/7zC.txt
Executable file
238
DOC/7zC.txt
Executable file
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7z ANSI-C Decoder 4.16
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----------------------
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7z ANSI-C Decoder 4.16 Copyright (C) 1999-2005 Igor Pavlov
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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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Read lzma.txt for informaton about license.
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Files
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---------------------
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7zAlloc.* - Allocate and Free
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7zBuffer.* - Buffer structure
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7zCrc.* - CRC32 code
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7zDecode.* - Low level memory->memory decoding
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7zExtract.* - High level stream->memory 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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7zMethodID.* - MethodID structure
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7zTypes.h - Base types and constants
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How To Use
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----------
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You must download 7-Zip program from www.7-zip.org.
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You can create .7z archive with 7z.exe or 7za.exe:
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7za.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 doesn't support separated "folder" items inside archive.
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But you still can use files that are in subfolders
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- It doesn't support empty files (size = 0) inside archive.
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- It reads only "FileName", "Size", and "CRC" information for each file in archive.
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- It supports only LZMA and Copy (no compression) methods.
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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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.7z Decoder can be compiled in one of two modes:
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1) Default mode. In that mode 7z Decoder will read full compressed
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block to RAM before decompressing.
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2) Mode with defined _LZMA_IN_CB. In that mode 7z Decoder can read
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compressed block by parts. And you can specify desired buffer size.
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So memory requirements can be reduced. But decompressing speed will
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be 5-10% lower and code size is slightly larger.
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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 alocated 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 ISzInStream interface */
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CArchiveDatabaseEx 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 InitCrcTable(); function to initialize CRC structures.
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3) call SzArDbExInit(&db); function to initialize db structures.
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4) call SzArchiveOpen(inStream, &db, &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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SzArchiveOpen 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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{
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UInt32 i;
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for (i = 0; i < db.Database.NumFiles; i++)
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{
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CFileItem *f = db.Database.Files + i;
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printf("%10d %s\n", (int)f->Size, f->Name);
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}
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}
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Extracting code:
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~~~~~~~~~~~~~~~~
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SZ_RESULT SzExtract(
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ISzInStream *inStream,
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CArchiveDatabaseEx *db,
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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 preevious 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 SzArDbExFree(&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 openning:
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- Temporary pool:
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- Memory for compressed .7z headers (if _LZMA_IN_CB is not defined)
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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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- 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 compressed solid block (if _LZMA_IN_CB is not defined)
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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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If _LZMA_IN_CB is defined, 7z Decoder will not allocate memory for
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compressed blocks. 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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EXIT codes
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-----------
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7z Decoder functions can return one of the following codes:
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#define SZ_OK (0)
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#define SZE_DATA_ERROR (1)
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#define SZE_OUTOFMEMORY (2)
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#define SZE_CRC_ERROR (3)
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#define SZE_NOTIMPL (4)
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#define SZE_FAIL (5)
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#define SZE_ARCHIVE_ERROR (6)
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LZMA Defines
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------------
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_LZMA_IN_CB - Use special callback mode for input stream to reduce memory requirements
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_SZ_FILE_SIZE_64 - define it if you need support for files larger than 4 GB
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_SZ_NO_INT_64 - define it if your compiler doesn't support long long int
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_LZMA_PROB32 - it can increase LZMA decompressing speed on some 32-bit CPUs.
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_SZ_ONE_DIRECTORY - define it if you want to locate all source files to one direcory
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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/support.html
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