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LZW Data Compression Library
For Turbo Pascal
(LZW4P)
USERS MANUAL
Version 1.2
March 1, 1993
This software is provided as-is.
There are no warranties, expressed or implied.
Copyright (C) 1993
All rights reserved
MarshallSoft Computing, Inc.
Post Office Box 4543
Huntsville AL 35815
205-881-4630 Voice / FAX
205-880-9748 Support BBS
LZW4P Users Manual Page 1
C O N T E N T S
Chapter Page
1.0 Introduction..............................................3
1.1 Distribution Files....................................3
1.2 Compiling the Library.................................4
1.3 User Support..........................................4
1.4 Installation..........................................5
2.0 The LZW Algorithm.........................................6
2.1 LZW Compression.......................................6
2.2 LZW Expansion.........................................7
2.3 LZW Implementation....................................7
3.0 Example Programs..........................................8
3.1 COMPRESS..............................................8
3.2 EXPAND................................................8
3.3 TEST_LZW..............................................9
3.4 MK_ARC................................................9
3.5 UN_ARC................................................9
3.6 SEE_ARC...............................................9
4.0 Reader & Writer Functions................................10
5.0 Library Functions........................................11
5.1 InitLZW..............................................11
5.2 TermLZW..............................................11
5.3 Compress.............................................12
5.4 Expand...............................................12
6.0 Error Codes..............................................13
6.1 EXPANSION_ERROR......................................13
6.2 CANNOT_ALLOCATE......................................13
6.3 INTERNAL_ERROR.......................................13
6.4 NOT_READY............................................13
7.0 Legal Issues.............................................14
7.1 Registration.........................................14
7.2 License..............................................15
7.3 Warranty.............................................15
8.0 Revision History.........................................16
9.0 Other MarshallSoft Computing Products for Pascal.........16
9.1 The Personal Communications Library for Pascal.......16
LZW4P Users Manual Page 2
1.0 Introduction
LZW4P consists of a variable code size implementation of the LZW
(Lempel-Ziv-Welch) algorithm for compressing and decompressing
data. LZW does particularly well on text files, achieving better
than a 50 % compression ratio for many files.
The LZW algorithm is considered to be one of the best general
purpose algorithms available today. The new high speed modems
that employ on-the-fly data compression (such as MNP 5.0 & the
V.42 bis international standard) use the LZW algorithm, as well
as such well known utility programs such as PKZIP.
The LZW4P library is designed to be used in a wide variety of
situations. Some of the possible uses include:
1) Compression and expanding files on disk.
2) Compressing files "on the fly" before sending over a modem,
and then expanding on the receiving end.
3) Compression of data files used by your application program such
as help files, graphics screens, etc. The compressed data files
are then expanded as they are loaded by the application.
1.1 Distribution Files
The distribution files are as follows:
1) LZW4P.DOC -- This documentation file.
2) LZW4P.INV -- Invoice file.
3) COMPRESS.PAS -- Data compression example program.
4) EXPAND.PAS -- Data expansion example program.
5) LZW4P.PAS -- Library unit interface.
6) TEST_LZW.PAS -- LZW test driver program.
7) MK_ARC.PAS -- File archiving program.
8) UN_ARC.PAS -- File un-archiving program.
9) RW_IO.PAS -- Reader/Writer I/O source file.
10) DIR_IO.PAS -- Directory I/O source file.
11) LZW_ERR.PAS -- Displays text error messages.
12) MEMORY.PAS -- Memory allocation functions.
13) HEX_IO.PAS -- Procedure to read & write hexidecimal.
14) LZW4PLIB.OBJ -- Library object file.
Registered users also receive:
1) LZW4PLIB.ASM -- Library source file.
2) MAKETPU.BAT -- Makes library object from source.
LZW4P Users Manual Page 3
1.2 Compiling the Library
If you are not running Turbo Pascal 6.0, you may need to recompile
the library unit as follows:
TPC LZW4P
The registered user can recompile the source code (source code is
provided in the registered version only) for the library as
follows:
MAKETPU
or
MASM LZW4PLIB.ASM,LZW4PLIB.OBJ /DPASCAL_MODEL;
TPC LZW4P
1.3 User Support
We want you to be successful in developing your application using
our libraries! We depend on our customers to let us know what they
need in a library. This means we are committed to providing the
best libraries that we can. If you have any suggestions or
comments, please write to us or give us a call.
If you are having a problem using LZW4P or any of our libraries,
call (205) 881-4630 between 5 PM and 9 PM CST Monday through
Friday. You can call at other times and leave a message, and call
back later during our regular business hours for a reply. You can
also FAX us at this same number at any time.
You may also call our 24 hour BBS at any time. The BBS will
contain the latest shareware version of LZW4P, messages, and other
related files. All files are in standard ZIP format. You can
leave a message on the BBS, and we will usually have a reply ready
for you within 24 hours. The dedicated telephone number is
205-880-9748. Set your modem for 1200 to 9600 baud, 8 data bits,
no parity, one stop bit.
The MarshallSoft Computing, Inc. newsletter "Comm Talk" is
published quarterly. It discusses various communications problems
and solutions using PCL (the communications library) as well as
related information such as data compression issues. Registered
users receive a one year comp