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Text File | 1992-03-23 | 13.5 KB | 416 lines

LZW Lib 1.1 by Doug Hurst 8912 Spur Road Springfield, VA 22153 <<<General>>> LZW Lib is a library of functions that will allow you to do, in your C programs, some of the things you can do from the DOS commandline with such programs as PKZIP and PKUNZIP, ARC, LHARC, etc. While I've titled the library LZW, your files can have any extension you desire. In fact, there is no default extension. You should be aware that these files will probably (read that assuredly) not be structurally compatible with the files created by any of the programs mentioned above. This library uses a fairly generic LZW data encoding algorithm, downloaded from a bulletin board, and allows you to create and manipulate files of encoded files. <<<The Theory of Operation>>> The encoded files created by LZW Lib functions have the following structure: ┌─────────────┐ │ File Header │ ├─────────────┤ │ │ │ │ │ │ │ │ │ │ │ Encoded │ │ File │ │ Data │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ ├─────────────┤ │ File │ │ Directory │ │ │ │(linked list)│ │ │ │ │ │ │ └─────────────┘ The File Header is made up of the following structure: typedef struct { char lzwid; unsigned int num_files; unsigned long linkpos; }LZW_HDR; When an existing file is opened, two steps occur immediately. The header structure is read from the top of the file and the lzwid member of this structure is checked. If lzwid is not 0x1A, an error is returned. If the file is determined to be a valid LZW Lib file, the second step is a seek to file position contained in the linkpos member, then the file directory is read and a linked list developed. The num_files is maintained all the time the file is open. The linked list fields are as follows: typedef struct { char marked; char path[60]; char name[13]; unsigned long filepos; unsigned long size; unsigned long length; unsigned int date; unsigned int time; }FIELDS,*FIELDSPTR; This is almost self-explanatory. The structure member 'marked' is used to speed up file operations. When a new file is added to the encoded file, the linked list is searched for files of the same name. If found, marked member is changed from a ' ' (0x20) to an '*' 0x42 for those files and the new file added to the end. These files are then ignored by other operations. The LZW_HDR structure member linkpos is then updated so the program knows where to go to write the file directory when operations have been completed. You may be thinking if you only mark the old file and add the new file, doesn't the encoded file get bigger? Well, yes it does. There is a function called lzwpurge() that handles this at a more opportune time for the program, such as when exiting. I don't know if this is the best way to handle this, but it's the way I handled it. I'm open to suggestions. Additional explanation of the theory of operation is contained int the functions Reference section below. <<<The Files>>> The following files are provided in the .ZIP file: LZW.DOC This document LZWIN.C Source for an LZW encoding program LZWIN.PRJ Borland C++ 2.0 project file LZWINB.MAK Borland C++ 2.0 make file LZWIN6.MAK Microsoft C make file LZWIN.LNK Microsoft C link response file LZWOUT.C Source for an LZW decoding program LZWOUT.PRJ Borland C++ 2.0 project file LZWOUTB.MAK Borland C++ 2.0 make file LZWOUT6.MAK Microsoft C make file LZWOUT.LNK Microsoft C link response file LZW.SRC A PDQHelp(tm) (see below) file LZW.H A required header file when using the library functions LZWLBC.LIB Large code library for Borland C 2.0 and above LZWMBC.LIB Medium code library for Borland C 2.0 and above LZWSBC.LIB Small code library for Borland C 2.0 and above LZWLC6.LIB Large code library for Microsoft C 5.1 and above LZWMC6.LIB Medium code library for Microsoft C 5.1 and above LZWSC6.LIB Small code library for Microsoft C 5.1 and above <<<The Functions>>> lzw_init() A must call before calling any other functions lzw_deinit() A must call beore exiting the program lzw() The encoding (in) function unlzw() The decoding (out) function lzwpurge() The tidy up function <<<The Future>>> I think this library will be useful for some applications. It is my intention to go through and speed things up with some in-line assembly wherever I can. It is also my intention to add to the library to allow encoded files to be decoded and placed directly into memory. Currently, you simply create a full-sized file, which you then have to open and read. I'm not sure how I'm going to do this yet, and again, I'm open to suggestions. <<<The Money>>> If you find this program useful and would like to donate to its contined life, I think a contribution of $10.00 would be sufficient for now. You can send it to the address contained at the top of this document. <<<The PDQHelp(tm) file>>> I'm sure most of you don't know about PDQHelp(tm). PDQHelp(tm) is the greatest on-line help program for programmer's ever. It's available from: Leverage Software 2241-R Tacketts Mill Rd WoodBridge, VA 22192 1-703-643-0818 It's a TSR but is very well behaved and takes up only 29K, and can be loaded high on 286's with QRAM or 386's with just about any high memory manager. Remember the The Norton Guides? It took up 70K. You can block/cut/paste into your editor or send to a printer. You can search by keyword, string within keyword, or scan the help text itself. You can also pick keywords off the screen. Help files can be as large as available disk space up to 100000 keywords and 1200 lines per keyword. Various help files can merged together to make consolidated help files. One I have consists of all the Vermont Views(tm), Greenleaf Comm, Advanced DOS, C 6.00A and Essential Graphics functions and other reference material. Very handy indeed. Greenleaf Software thinks enough of it to supply PDQHelp(tm) files for all their libraries I swear to you if you ever use this program, you'll never want to be without it. Enough of my swearings. <<<Miscellaneous>>> Since I use both Borland C++ and Microsoft C, I use a directory called \OTHERINC to hold the header files for third party libraries so I don't have to have duplicate copies. You will likely have to change the paths in the make files for LZWIN.C and LZWOUT.C to get them to compile and link properly. Doug Hurst ================================================================= <<<Reference>>> ----------------------------------------------------------------- LZW_INIT() lzw_init() Initializes the LZW library #include <lzw.h> void lzw_init(); Returns None Description This routine initializes certain global variables Cautions This function MUST called before calling any other LZW library functions. Related Functions ----------------------------------------------------------------- LZW_DEINIT() lzw_deinit() Deinitializes the LZW library #include <lzw.h> void lzw_deinit(); Returns None Description This function clears the linked list. Cautions This functions must only be called after a call to lzw_init() Related Functions lzw_init() ----------------------------------------------------------------- LZW() lzw() Encodes file(s) into an LZW file #include <lzw.h> int lzw(char *lzw_pathfile, unsigned long ops, char *infile_pathmask); Returns 0 Success -1 Could not open or create LZW file -2 Not an appropriate LZW file -3 Could not read in file directory (linked list) -4 Nothing to do. _dos_findfirst on mask unsuccessful -5 Could not open input file -6 Encoding error -7 Could not save file directory (linked list) Description This function acts on the lzw_pathfile to perform the specified ops: PATHNAMES - May be used to insert the entire pathname of the file into the LZW header. The infile_pathmask parameter is the mask of files that are to be encoded and may include a valid DOS path. A pass is made through the entire .LZW file, skipping from header to header, for each file to be encoded. If that file already exists, the header structure member 'marked' is filled with the '*' character, then the new file is appended to the end of the file. This can cause the .LZW file to grow fairly rapidly in size because the old files are not automatically purged. The lzwpurge() function may be used to physically purge all marked files. Related Functions unlzw(), lzwpurge() ----------------------------------------------------------------- UNLZW() unlzw() Decodes file(s) from an LZW file #include <lzw.h> int unlzw(char *lzw_pathfile, unsigned long ops, char *mask); Returns 0 Success -1 Could not open LZW file -2 LZW file is empty or corrupted -3 Not an LZW file -4 Could not load file directory (linked list) -5 Could not create output file -6 Decoding error -7 Could not save file directory (linked list); Description This function acts on the lzw_pathfile to perform the specified ops: EXTRACT - Extracts the files designated by the parameter mask. VIEW - Not currently implemented, but will allow the passing of a function pointer to give the programmer access to file information designated by the parameter mask. Cannot be used in conjunction with any other operation. CREATEDIRS - Can be used in conjunction with the EXTRACT operation to create the directory specified in the path structure member, if such a path exists. NOOVERWRITE - Can be used in conjunction with EXTRACT and/or CREATEDIRS so existing files will not be overwritten. Otherwise, they will be. Only files matching the mask parameter will be extracted. Caution Ops may be or'd together for this call, except that the VIEW option MAY NOT be used in conjunction with any other call. Related Functions lzw() ----------------------------------------------------------------- LZWPURGE() lzwpurge() Purges marked and specified files from an LZW file #include <lzw.h> int lzwpurge(char *lzw_pathfile,char *mask); Returns 0 Success -1 Could not LZW file -2 Not an appropriate LZW file -3 Could not open temporary file Description This call will purge all 'marked' files from lzw_pathfile. Specifiying a mask will also cause files matching the mask to be purged even if they have not been previously marked. Pass NULL in the mask parameter position if no additional files are to be purged. Related functions lzw()