Dec 062017
 
PD file compress/decomp. program with Turbo Pascal 5 source.
File MDCD10.ZIP from The Programmer’s Corner in
Category Pascal Source Code
PD file compress/decomp. program with Turbo Pascal 5 source.
File Name File Size Zip Size Zip Type
LZ.MD 13245 12542 deflated
MDCD.DOC 43276 12690 deflated
MDCD.EXE 51107 24655 deflated
MDCD.PAS 65020 12500 deflated
MDCD1213.ASM 60995 10516 deflated
MDCD1213.OBJ 3232 2299 deflated
TESTC.PAS 7546 1867 deflated
TESTD.PAS 7390 1794 deflated
TIMING.DOC 7555 2151 deflated

Download File MDCD10.ZIP Here

Contents of the MDCD.DOC file



MDCD Version 1.0 - 10/24/88 - File Compression and DeCompression Program

This documentation is organized in the following order, under the
following headings:

WHAT IS IT ?
WHAT ISN'T IT ?
WHY WAS IT WRITTEN ?
HOW CAN I USE IT ?
WHAT ARE THE RESTRICTIONS ?
CONCERN # 1
CONCERN # 2
CONCERN # 3
CONCERN # 4
MDCD GENERAL INFORMATION & FEATURES
MDCD COMPRESS OPTION
MDCD DECOMPRESS OPTIONS
MDCD LIST OPTIONS
MDCD FUTURE RELEASES
SOFTWARE DESCRIPTION
WRITING YOUR OWN PROGRAMS
THE COMPRESSION ALGORITHM
MISCELLANEOUS INFO
LIABILITY
DISCLAIMERS
ACKNOWLEDGEMENTS
WHERE CAN I GET THE MOST RECENT COPY OF THE SOFTWARE ?
WHERE CAN I CONTACT THE AUTHOR ?


WHAT IS IT ?

MDCD 1.0 is the first release of a file compression and
decompression program that compresses data using a 13 bit LZW
algorithm. It was written in Turbo Pascal and requires the
Turbo Pascal 5.0 compiler. Portions are written in 808x
assembler and require Turbo Assembler 1.0 or MASM 3.0+.

It is not as fast as PKWARE products but compresses almost as
well. It is significantly faster and compresses better than
the only version of ARC that I could find to compare it
against (version 5.20).

It demonstrates some interesting differences when compared to
current file compression/decompression programs. I will talk
about the differences in a bit, but first I want to talk
about what it is not...


WHAT ISN'T IT ?

It is not a replacement for PKWARE/SEA products. It is not a
solution to the ARC wars that currently have (to mention a
few) BBS Sysops, telecommunications networks and PC users in
general in total disarray. It is not meant to show off my
computer knowledge as I am terrible when it comes to math,
and have only a simplistic understanding of the compression
algorithm involved.

You are probably asking yourself, "Then why was it written" ?
I shall explain...


WHY WAS IT WRITTEN ?

I write commercial PC software for a living. This includes a
specialized communications program, a telephone call
accounting system and several clients that require low level
systems programming. The communications program uses
compression in the process of preparing files for
transmission. The call accounting system is rather large and
I need to reduce disk storage and increase reliability when
shipping and installing. I also like to have an orderly
method of keeping track of various releases and revision
levels of this software.

I did not want to pay an exorbitant fee to license
compression technology from a third party. Not only is this
cost prohibitive for someone trying to make a simple living,
but it is nearly impossible to get
something that can be tailored to ones own needs. You are
stuck with a program that more than likely requires more disk
space, or gobbles up more quantities of memory than you care
to relinquish.

So, I wrote my own. It is written for my needs. It uses
minimal memory. It requires no disk work area. It allows me
to remember the exact path that a file was compressed from.
It lets me store comments about the file. It lets me keep
duplicate file names in a compressed file, retaining their
real-time chronological order. It lets me remember the
original file's date, time and size. It allows me to retain
a file's original attributes so that if it is a hidden,
system, read only file before compression, it will be
likewise after. It allows me to simply group files together
in a single area and doesn't waste time trying to compress
already compressed .ARC or .ZOO files. It serves my exact
needs and is written for me, a commercial software author, to
facilitate control and distribution of software.

I wrote it for one other express purpose. I continually grow
in my programming abilities. I have been programming
computers for over 20 years and can't think of any period in
my career where I wasn't constantly increasing my knowledge
and awareness of current computer technology. This has
happened at a fairly logical pace for most of my programming
life... Until I discovered the crazy world of
telecommunications/public domain/shareware/BBS'ing/networks in
the sky/etc./etc.

This crazy world has increased my knowledge, solved my
day-to-day technical problems, provided my with one heck of a
lot of fun and exposed me to computer technology at a rate I
would never have believed possible. I have learned from the
generosity of others sharing their knowledge, experience and
brilliance and I want to attempt to repay that in kind.

"So", you ask yourself, "how can I use this software?"


HOW CAN I USE IT ?

You can use it in any way that it serves your needs, providing
you adhere to a couple of restrictions I will talk about in a
minute. I am including all of the source code. If you are a
shareware, or commercial software author, you could probably
use it in many of the ways I mentioned above. Some ideas that
come to mind:

A communications program compression of files prior to
transmission. Graphics compression while saving to disk.
Word processor document compression. Distributing products
in compressed format and reliably determining a successful
installation. Personal file compression program.
Maintaining version/release control of software products,
word processing documents, or just about anything. To
mention a few!

"Hmmmmm, sounds like I could use this, but what ARE those
restrictions ?"


WHAT ARE THE RESTRICTIONS ?

I toyed with the idea of copyrighting this software. I
wanted to somehow have a means to control the few
restrictions & requests that I had decided on. But that
seemed kind of silly, and basically unenforceable. I was
modifying a brilliant algorithm (which I do not understand),
written by someone else (who had placed the code in the
public domain) and adding some simple stuff to move some
files around and keep track of basic information. And on top
of that I was releasing the source to the general public,
virtually no strings attached! I figured that I would get
thrown out by any court trying to decide if my copyright was
enforceable, especially if the proprietary source code was
made available to all. So... NO COPYRIGHT.

I have three restrictions. All are unenforceable legally, one
is enforceable morally, the other two are enforceable by virtue
of the media in which this is distributed.

Restriction 1: If you use this code as part of a product that
you gain monetarily from, I will be considered a "registered"
user of that product, with all related privileges. In other
words, you send me current releases of your product. If you
have a BBS that supports your product and charge a related
fee, I will be able to use it. If you have a quarterly
newsletter, I will receive a copy. I consider this enforceable
morally as I find it difficult to believe that any shareware
or commercial organization would prohibit unauthorized use of
their own software and yet violate this principle in using
other's software against stated restrictions. (is he naive,
you ask?)

Restriction 2: You may not use this code to create a product
that competes with existing compression programs, shareware or
otherwise. I do not want to be part of, or contribute to, the
mass confusion that currently exists over conflicts between
SEA and PKWARE. I will not delve into this issue in this
document, but please KNOW that I see RED every time I think of
the grief and chaos that this issue is causing a whole world
full of users. This is somewhat enforceable in two ways.
Number 1, if you are discovered by the public in general, your
product will not be supported, and number 2, if I find out
about it, I will make it common knowledge on every BBS and
major network in this country. And believe me, tenacity and
relentless are my two middle names. (yup... he's naive!)

Restriction 3: If you distribute this software, don't charge
for it. Charges for postage & handling (that are in line with
currently prevailing rates for shareware & public domain
software) or connection and access charges to commercial
networks or pay BBS's are excluded from the "don't charge for
it" portion of this restriction. Make sure that it is
distributed in the same form that you received it in. Do not
remove or modify any of the files. This is enforceable in the
same manner as restriction 2 discussed above.

"Okay, I want to use it, and I agree to the restrictions,
... BUT I have some concerns".



CONCERN # 1

"I am concerned about the legality of using this software."

If you have second thoughts about using this software in your
commercial or shareware products, and are worried about not
REALLY having my permission, write me a letter stating that
you would like express permission to use this software, and
state that you will adhere to the restrictions outlined above.
I will send you my permission on (what do they call that
stuff?? oh yeh..) paper giving you the authority to use the
programs in any way you see fit.


CONCERN # 2

"I'm not sure I'm up to modifying this compression stuff."

If you're not sure you want to get into the complexities of
writing or adapting compression technology to your software
products, I will make myself available to you (after all, this
IS how I feed my rug rats!) on a consulting basis. While
generating direct revenue was not a consideration for creating
this product, I would rather enjoy the task of adapting this
software in unique areas.


CONCERN # 3

"Does this stuff really work?"

I have tested it as extensively as I can. That means that the
first person to try it will probably find everything I missed,
and then some. I have also had 5 other people putting it
through its paces. So far, no problems. I have included
extensive disk error checking. Throughout the entire
development process, I did not once wipe out any of my disk
files, or create any cross-linked clusters, and most of the
disk I/O is done in assembler. I attribute this to 1)
starting with an working public domain program, 2) extensive
disk error checking, 3) Turbo Pascal's extensive error
checking, and 4) extreme caution and care on my part.


CONCERN # 4

"I've heard about them VIRII. Am I taking a chance?"

All of the source code is included. Look at it, recompile it
yourself, and test it in your own carefully created
environment.


MDCD GENERAL INFORMATION & FEATURES

MDCD has three basic functions. It allows you to compress a
file or files, decompress a previously compressed file or
list the directory of files contained within a compressed
file.

Typing MDCD with no parameters or entering an invalid command
will display a help screen.

MCDC is a program that provides a fairly functional
compress/decompress program. It was written to test and
exercise the core routine that does that actual
compression/decompression (MDCD1213.ASM). The source code
provides excellent examples for writing your own compression
program or routines.

Some of the features, and lack thereof are:

- Uses 13 bit LZW compression.

- Original file date, time, and attributes are preserved.

- Compress file extensions default to .MD if not specified.

- Files added to an existing Compress file are appended to
the end of the file.

- Because duplicate files are allowed, and because files are
added in physical order, an inherent ability to keep a
chronological backups of files is available.

- File headers are added in the order that files are added to
the Compress file. Therefore Compress file directory lists
will not be in alphabetical order as you are probably used
to. They will be in the same order that you added files to
the Compress file.

- No external disk work space is required for any functions.

- The program is fairly small. 39k for Code, 1k for Date, 3k
for Stack and 45k for heap for a total of 88k. Using 12
bit compression would reduce the program size by 20k
requiring 68k total memory.

- The complete drive:path\name is kept for every compressed
file.

- 122 bytes of overhead is incurred for each file stored in a
compress file. Most of this is for the original
drive:\path\name. I chose to do this on the first release
because having this information available is much more
valuable than the related disk space required.

- If a file does not compress smaller than the original, it
is stored as is, retaining its original size.

- .ZOO and .ARC files are automatically recognized, and no
attempt at compression is performed. The file is stored as
is.

- Conventional DOS wildcards may be used when specifying
files to be compressed.

- MDCD will not inadvertently try and compress the file that
is currently being output to.

- MDCD will, at this time, only decompress an entire Compress
file.




MDCD COMPRESS OPTION

This option allows you to compress a single or multiple
files. You can compress to a new file, or existing file.
Additions are always made to the end of the file. The
compress file may contain exact duplicate
drive:\path\filenames. If you attempt to compress to an
existing file, a validity check is made prior to any physical
writing to the file. If it is determined not to be a
compress file, you will be informed and the program will
terminate. Three (3) parameters are required:

Parameter 1: This parameter always contains the option. In
the case of compression it must be 'C'.

Parameter 2: File to be compressed. This may contain a
complete drive:\path\ name in front of the file name. If no
drive: or path\ is specified, the currently directory will
be searched. Valid DOS wild cards are allowed.

Parameter 3: File to contain the compressed input file. If
pre-existing, it must be a valid compress file. If not
found, it will be created. It may contain a complete
drive:\path\name in front of the file name. The drive:\path\
is verified for existence. If no drive: or path\ is
specified, the currently directory will be used. If no file
extension is specified, the extension of .MD will be
appended. If you wish no file extension for the file, end
your file name with a period. e.g. [COMPFILE.].


MDCD DECOMPRESS OPTIONS

There are two different decompress options allowing the
decompression of all files in an existing compress file.
They are identical except that the 'D' option will pause and
prompt you if it encounters an existing file of the same name
as one it is about to decompress. The 'R' option will
automatically 'R'eplace any files it decompresses, informing
you with a message, but no pause.

If you attempt to decompress a nonexisting file, you will be
informed. if you attempt to decompress an existing file, a
validity check is made. If it is determined not to be a
compress file, you will be informed and the program will
terminate. Two (2) or three (3) parameters may be specified:

Parameter 1: This parameter always contains the option. In
the case of decompression, it must be 'D' or 'R'. Specifying
'D' will cause a pause and prompt to occur if the program
attempts to decompress a file that currently exists. You may
respond with 'Y'es to replace the file or any other key to
ignore the file and go on. Specifying 'R' will automatically
replace any pre-existing files encountered.

Parameter 2: File to be decompressed. This may contain a
complete drive:\path\ name in front of the file name. If no
drive: or path\ is specified, the currently directory will
be searched. If no file extension is specified, the
extension of .MD will be appended. If you wish no file
extension for the file, end your file name with a period.
e.g. [COMPFILE.].

Parameter 3: Drive:\path to contain the decompressed output
files. This parameter may be left blank, in which case files
are decompressed to the current directory. if a drive:\path\
is entered, it is verified for existence. one slight problem
exists when specifying the path. If you specify an output
drive:\path to decompress to and it is specifying other than
that root directory, you must leave off the trailing '\'. In
other words, if you want to decompress to the root directory
of your C: drive, enter c:\ - if you want to decompress to a
subdirectory off your root directory on your c: drive, enter
C:\SUBDIR - do NOT enter c:\subdir\. I will fix this in the
next release.


MDCD LIST OPTIONS


There are two different list options. they both allow you to
display a directory of all of the files in an existing
compress file. They are identical except that the 'l' option
displays original file date and time information and the 'F'
option displays the original file drive:\path\ in its place.

If you attempt to list a nonexisting file, you will be
informed. if you attempt to list an existing file, a
validity check is made. if it is determined not to be a
compress file, you will be informed and the program will
terminate. Two (2) parameters are required:

Parameter 1: This parameter always contains the option. In
the case of list, it must be 'l' or 'f'. both options will
display a directory of all compressed files contained in a
compress file. Specifying option 'l' will cause the original
file's date and time to be displayed. specifying option 'F'
will cause the original file's drive:\path to be displayed
instead of the date/time.

Parameter 2: File to be listed. this may contain a complete
drive:\path\ name in front of the file name. If no drive:
or path\ is specified, the currently directory will be
searched. If no file extension is specified, the extension
of .MD will be appended. if you wish no file extension for
the file, end your file name with a period. e.g.
[COMPFILE.]. Wildcards can not be currently used to specify
multiple compress files to be listed. This will be addressed
in the next release.

Output may be redirected with the > and >> redirection
symbols.


Example of entering: MD L LZ

Compressed File: LZ.MD

ORIG CMP HDR cmp cmp prg
FILE NAME SIZE SIZE LEN pct typ ver crc date TIME
-------------------------------------------------------------------------
LZ.TXT 3615 1965 122 45% lzw13 10 ecae 07-01-86 13:23:56
LZCOMP.ASM 7261 3703 122 48% lzw13 10 fc76 07-01-86 14:02:44
LZCOMP.EXE 3607 678 122 80% lzw13 10 a6ce 07-01-86 14:04:24
LZDCMP.ASM 6094 3152 122 47% lzw13 10 4c26 07-01-86 14:02:12
LZDCMP.EXE 3620 670 122 80% lzw13 10 8d01 07-01-86 14:04:18
MACROS.MLB 6422 2345 122 62% lzw13 10 45ca 06-30-86 14:12:34
------ ------ ----- --
30619 12513 732 59%



Example of entering: MD F LZ

Compressed File: LZ.MD

ORIG CMP HDR cmp cmp prg
FILE NAME SIZE SIZE LEN pct typ ver crc original pATH
-------------------------------------------------------------------------
LZ.TXT 3615 1965 122 45% lzw13 10 ecae j:\lzw\original\
LZCOMP.ASM 7261 3703 122 48% lzw13 10 fc76 j:\lzw\original\
LZCOMP.EXE 3607 678 122 80% lzw13 10 a6ce j:\lzw\original\
LZDCMP.ASM 6094 3152 122 47% lzw13 10 4c26 j:\lzw\original\
LZDCMP.EXE 3620 670 122 80% lzw13 10 8d01 j:\lzw\original\
MACROS.MLB 6422 2345 122 62% lzw13 10 45ca j:\lzw\original\
------ ------ ----- --
30619 12513 732 59%


MDCD FUTURE RELEASES

MDCD will be an evolving product. Items that are on my to do
list to be addressed are:

- Ability to sort several ways when doing a compress file
directory list.

- Various length header records to allow a smaller header
record without the drive:\path\, one to allow a file
comment to be attached to each file and one to allow a file
description to be attached to each file (variable length).

- Ability to override file compression and force file(s) to
be stored directly.

- Ability to disable the saving/restoring of original file
attributes.

- Ability to compress and decompress an entire disk(ette), or
sub-directory and all lower level sub-directories,
maintaining original disk(ette) structure.

- Ability to force decompression to the original
drive:\path\.

- Program to allow the creation of self-extracting compress
files.

- Ability to decompress individual files and selected file(s)
that have duplicate names.

- Fix the irritation when using append or similar TSR's where
a file appears to already exist, but doesn't.

- Allow wildcards to be used for decompressing and
listing multiple Compress files.

- Implement heuristic logic and user specified requests
allowing the use of both 12 bit and 13 bit compression.

- Change MDCD1213.ASM to allow simpler interface with Turbo C
and various models.


SOFTWARE DESCRIPTION

The compressed file you received should contain the following
files:

LZ MD 13245 10-26-88 12:52a
MDCD DOC 43168 10-26-88 12:55a
MDCD EXE 51107 10-26-88 12:52a
MDCD PAS 65020 10-26-88 12:52a
MDCD1213 ASM 60995 10-26-88 12:52a
MDCD1213 OBJ 3232 10-26-88 12:52a
TESTC PAS 7546 10-26-88 12:52a
TESTD PAS 7390 10-26-88 12:52a
TIMING DOC 7555 10-26-88 12:52a


A simple description of each file:

LZ.MD - Original .asm/.exe for lzcomp & lzdcmP.
Compressed with MDCD.

To see a list of files:

MDcd l lz (show original date/time)
MDcd f lz (show original path)

To decompress to current subdirectory:

MDcd d lz

MDCD.DOC - Documentation and other information.

MDCD.PAS - Source for MDCD 1.0.

MDCD.EXE - Executable MDCD 1.0.

MDCD1213.ASM - Source for the assembler compress &
decompress functions.

MDCD1213.OBJ - Linkable module for compress & decompress
functions.


TESTC.PAS - Simple single file compression illustrating
the use of MDCD1213.obj assembler module.

TESTD.PAS - Simple single file decompression illustrating
the use of MDCD1213.obj assembler module.

TIMING.DOC - Timing/compression size comparison between
MDCD 1.0, PKPAK/PKUNPAK 3.61, and ARC 5.20.



WRITING YOUR OWN PROGRAMS

MDCD1213.ASM is the compression/decompression algorithm
routine. It can be compiled with TASM 1.0 or MASM 3.0 and
up. It creates MDCD1213.obj. it has two routines which may
be called. These routines are compressfile & decompress
file. Each is a FAR assembler proc. make sure you identify
these calls as FAR in your high level language. They are
both implemented as high level language functions in that
they pass back a WORD/INT/DW value indicating the success of
the request. They also pass back a RECORD/STRUCT/STRUCT that
contains either the compressed file crc and size, or the
decompressed file crc and size. It is up to the caller to
determine if the crc is correct. This assumes that the user
of this routine has implemented his/her own internal file
structure.

To call CompressFile, or DecompressFile, you need to pass
several parameters on the stack. The parameters are the same
for both functions however their meaning is a bit different
depending on which routine you are calling. For a more
detailed description of the parameters, see the listing for
MDCD1213.ASM or look at TESTC.PAS, or TESTD.pas. These
parameters are described below and are pushed onto the stack
in the order described:

Parameter 1: This is a valid dos file handle for the input
file. The file must be currently opened under this handle.
For CompressFile, this is the individual file to be
compressed. For DeCompressfile, this is the file that is to
be decompressed.


Parameter 2: This is a valid dos file handle for the output
file. The file must be currently opened under this handle.
For CompressFile, this is the compressed output file. For
DeCompressFile, this is the name that you want to call the
file after it is decompressed.


Parameter 3: This is the LONGINT/LONG/DD value that
specifies the byte offset within the input file that you want
to start decompressing at. This is provided so that you may
include multiple files in a compressed file. See MDCD.PAS
for an example. MDCD1213.ASM specifies this parameter as two
word values, but to the caller, it is strictly a double word
long value. If you are only compressing and compressing
single files, this value will always be zero (0).


Parameter 4: This is a @POINTER/&POINTER/SEGMENT:OFFSET that
points to a RECORD/STRUCT/STRUCT defined in the callers
program. MDCD1213.ASM specifies this parameter as two word
values, but to the high level language caller this is
strictly a single far pointer. To an assembler programmer,
the first parameter is the segment and the second parameter
is the offset. This area will receive return data from
CompressFile or DeCompressfile. This record needs to contain
5 bytes allocated as a WORD/INT/DW and a LONGINT/LONG/DD.
For CompressFile, the compressed file's crc and size in bytes
is returned. For Decompressfile, the decompressed file's CRC
and size in bytes is returned. These structures should look
something like this, depending on your language:

{--------} /*-----*/
{ PASCAL } /* c */
{--------} /*-----*/

Type
ReturnRec = Record struct returnrec {
FileCrc : Word; int filecrc;
FileSize : Longint; long filesize;
end; } returnr;
Var
ReturnR : Returnrec;

;-----------;
; ASSEMBLER ;
;-----------;


returnr struc
filecrc dw ?
filesize dd ?
returnr ends

Parameter 5: This is a WORD/INT/DW containing the segment
address of a contiguous area of memory used for storing the
temporary hash table. the size of this area varies depending
on whether you are using 12 or 13 bit compression, and
depending on the routine being called:

CompressFile 12bit 20480 bytes
CompressFile 13bit 40960 bytes
DeCompressFile 12bit 12288 bytes
DeCompressFile 13bit 24576 bytes


Parameter 6: This is a value indicating the type of
compression or decompression to be performed. This value
MUST be 12 for 12 bit or 13 for 13 bit. The values are not
checked, and an incorrect value will more than likely lunch
your machine.


In the event of a severe error in the MDCD1213.OBJ module,
control will be passed back to the caller (after cleaning up
the stack) and a function return code of $ffff/0xffff/0ffffh
will be returned. The SS & SP, registers and the number of
parameters on the stack are stored upon entry so that
MDCD1213.OBJ can unwind itself no matter what routine the
error occurs in and perform a far jump back to the caller.

For a simple example of using MDCD1213.OBJ see the included
files TESTC.PAS and TESTD.PAS. TESTC.PAS allows you to
compress a file by entering:

TESTC [uncompressed_file_name] [compressed_file_name]

TESTD allows you to decompress a file by entering:

TESTD [compressed_file_name] [uncompressed_file_name]

NOTE: MDCD1213.ASM needs to be changed to interface with
Tubro C. It currently is model sensitive and the parameters
would have to be passed backwards, or with pascal calling
conventions. The segment names would have to also agree to
Turbo C conventions.



THE COMPRESSION ALGORITHM

The compression algorithm is contained in MDCD1213.ASM. It is
an extensively modified version of Tom Pfau's LZCOMP & LZDCMP
programs written in 808x assembler. It provides for 12 bit
and 13 bit LZW compression. Tom's original programs are
contained in this download.

Tom's original source implemented the Lempel-Ziv-Welch 12 bit
compression with non-repeat packing. The initial size of the
code started at 9 bits and proceeded to a maximum code size
of 12 bits. Once the number of codes exceeded the current
code size, the number of bits was increased. When the table
filled (4096 entries), a clear code was transmitted for the
decompression routine and the table re-initialized, starting
over at 9 bits. The maximum of 12 bits allowed 4096 codes.
This algorithm is referred to as "Crunched" (note the UPPER
case 'C') in several compression programs.

I modified the code to also allow for a maximum of 13 bits, or
8192 codes. Other than that, it is identical to 12 bit
compression. This algorithm is referred to as "Squashed" in
several compression programs.

The original source of the algorithm is from the article "A
Technique for High Performance Data Compression" by Terry A.
Welch which appeared in IEEE Computer Volume 17, Number 6
(June 1984), pp 8-19.


MISCELLANEOUS INFO

MDCD1213.ASM uses the same 16 bit CRC used by communications
programs.

If MDCD1213.ASM encounters a corrupted file during
decompression, or if invalid parameters are passed to it
(e.g. 12 bit when it was actually compressed using 13 bit),
your machine will probably go to lunch. I will work on
trying to recognize these problems and finding a solution
that allows for a graceful exit.

All of the included source code is HEAVILY commented... Maybe
even excessively. This should help to make it more
understandable for anyone attempting to utilize it in their
own software tools.

My tests of the 12 vs. 13 bit compression show that .EXE
files are an average of 1/2 of 1% smaller using 12 bit.
Most other files, especially text type files will be anywhere
from 4% - 7% larger. This is why I chose to implement the 13
bit LZW compression option in MDCD.



LIABILITY

LIMIT OF LIABILITY

MDCD and its related source code is distributed as-is. The
author disclaims all warranties, expressed or implied. The
author will assume no liability for damages either from the
direct use of this product or as a consequence of the use of
this product.



DISCLAIMERS

I have NOT looked at the source code for ARC, ZOO, DWC or any
other file compression programs other than the original
LZCOMP/LZDCMP assembler code, in the process of designing or
programming this software. I have not used any existing ARC,
ZOO or DWC documentation to assist in the design of file
formats or file stowage methodologies. I have purposefully
avoided any likeness to existing file compression programs
that I have knowledge of. I have used the command line to
pass parameters to my program. If THIS ever becomes a
"look-and-feel" issue, we are ALL in big trouble.

I HAVE looked at hex dumps of both ARC and ZOO files to
determine how to identify them as such, so that I can avoid
the compression cycle and subsequently store the file. This
is limited to finding a commonality that identifies these
files, and in both cases, is determined by the file
extension, along with the first character stored in the file.
This information was NOT garnered from ARC/ZOO file
documentation.

This program will NOT extract files from ARC or ZOO files or
compress files into existing ARC or ZOO files. It WILL store
an ARC or ZOO file into my .MD files as it will ALL files.



ACKNOWLEDGEMENTS

We walk on the shoulders of others that came before us, or
however that old cliche goes.. I want to acknowledge several
people who have contributed directly or indirectly to this
program; most, if not all of whom have never heard of me.
Please forgive any omissions:

Terry A. Welch, for the compression algorithm.

Tom Pfau, for LZCOMP & LZDCMP.

SEA & PKWARE (in a convoluted way), for creating the
atmosphere that "incited" me to write this thing.

TurboPower Software, for the highest quality programming tools
and a refreshingly unique commitment to professionalism and
business practices.

Jerry D. Stuckle for the ASYNC.ASM tutorial, from which I
learned 808x assembly and the 8250.

Phil "PIB" Burns for PIBTERM, from which I learned many
excellent Turbo Pascal techniques and overcame communications
hurdles.

Ray Duncan for "Advanced MSDOS Programming", Microsoft Press,
without which, life would have been much more complex.

Jim Kyle, Chip Rabinowitz, Ray Duncan & other contributors to
"The MS-DOS Encyclopedia", Microsoft Press, a formidable
reference to Ms. DOS and all her idiosyncracies.

Neil Rubenking, for once helping me with a simple (to him),
yet insoluble (to me) problem, saving me untold hours.

Philippe Kahn and Borland International (a deity??) for
consistently producing the highest quality software, and the
most reasonable prices, and providing support to boot! (Thank
you CIS and BPROGA)

And.. last, but not least (don't the wife and kids ALWAYS
come last ?, just ask'm!)

Emilie, Matthew, Michelle and Melissa, for putting up with my
idiosyncracies, long hours, and my mistress: the computer.



WHERE CAN I GET THE MOST RECENT COPY OF THE SOFTWARE ?

The software will be evolving. Current copies may be obtained
from:

(preferred)

1. Amiga Techniques + PC Tech BBS - (GT POWER)
(209) 298-8453 - 1200-9600 HST (24 hours)

2. Compuserve
(BPROGA, IBMPRO, IBMAPP, PCMAGNET, CONSULT, PROGFORUM)

3. EXEC PC BBS

(if you're desperate)

4. Send a self-addressed, postage paid mailer to me
plus $1.00 for diskette.

5. Send $3.00 and I will provide the diskette and postage.
Please don't request FED-EX or UPS.



WHERE CAN I CONTACT THE AUTHOR ?

I may be contacted (in order of preference) at the locations
(electronic or otherwise) listed below:

Amiga Techniques + PC Tech BBS - (GT POWER)
(209) 298-8453 - 1200-9600 HST (24 hours)
Directly or through NET mail node 014/000.

CIS: 76676,1362
(BPROGA, IBMPRO, IBMAPP, PCMAGNET, CONSULT, PROGFORUM)
(BPROGB, IBMSYS, IBMCOM)

GENIE: MDAVENPORT

Mike Davenport
Mike Davenport & Associates
6751 N. Blackstone Ave. Suite 252
Fresno CA 93710

Voice: (209) 298-8846



 December 6, 2017  Add comments

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