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LZW Data Compression Library
For the C Language
(LZW4C)
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
LZW4C 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.........................................15
9.0 Other MarshallSoft Computing Products for C..............16
9.1 The Personal Communications Library for C............16
9.2 The Personal Protocol Library for C..................16
LZW4C Users Manual Page 2
1.0 Introduction
LZW4C 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 LZW4C 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) LZW4C_C.LIB -- COMPACT model library.
2) LZW4C_L.LIB -- LARGE model library.
3) LZW4C_L.MIX -- LARGE model library (MIX only).
4) LZW4C.DOC -- This documentation file.
5) LZW4C.INV -- Invoice file.
6) COMPRESS.C -- Data compression example program.
7) EXPAND.C -- Data expansion example program.
8) LZW4C.H -- Library prototypes.
9) TEST_LZW.C -- LZW test driver program.
10) MK_ARC.C -- File archiving program.
11) UN_ARC.C -- File un-archiving program.
12) SEE_ARC.C -- Program to list archived files.
13) *._T_ -- Turbo C makefiles.
14) *._M_ -- Microsoft C makefiles.
15) X_*.BAT -- MIX Power C batch file.
16) RW_IO.C -- Reader/Writer I/O source file.
17) RW_IO.H -- Reader/Writer prototype file.
18) DIR_IO.C -- Directory I/O source file.
19) DIR_IO.H -- Directory I/O prototype file.
20) SAYERROR.C -- Displays text error messages.
Registered users also receive:
1) LZW4C.ASM -- SOURCE CODE for the LZW4C libraries.
2) MAKE_C.BAT -- Batch file to make LZW4C_C.LIB
3) MAKE_L.BAT -- Batch file to make LZW4C_L.LIB
4) MAKE_XL.BAT -- Batch file to make LZW4C_L.MIX
LZW4C Users Manual Page 3
1.2 Compiling the Library
LZW4C requires rather large work buffers at run time. This
requires "far" data pointers which in turn means that you must
compile using either the COMPACT memory model (with "near" code
pointers) or the LARGE memory model (with "far" code addresses).
There are, therefore, two memory model libraries provided:
lzw4c_c.lib -- Compact memory model library.
lzw4c_l.lib -- Large memory model library.
lzw4c_l.mix -- Large memory model library (MIX only).
The registered user can re-compile the source code (source code is
provided in the registered version only) for the library using one
of the two provided batch files:
make_c.bat -- Creates lzw4c_c.lib.
make_l.bat -- Creates lzw4c_l.lib.
make_xl.bat -- Create lzw4c_c.mix.
Using the COMPACT memory model will result in a slightly smaller
and faster executable than using the LARGE memory model. Be sure
to compile all of your code for the correct memory model. Refer to
your compiler manual for more information on memory models.
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 LZW4C 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 (2400 baud, no parity, 8 data
bits, 1 stop bit) at any time. The BBS will contain the latest
shareware version of LZW4C, 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 PCL4C (the communications library) as well as
related information such as data compression issues. Registered
users receive a one year complimentary subscription when first
registering and for each update purchased. Additional one year
subscriptions are $15 plus $5 for overseas postage (postpaid in
US).
LZW4C Users Manual Page 4
1.4 Installation
(1) Microsoft C, Borland & Turbo C, and MIX Power C compilers are
supported. However, the code should work with most any C compiler.
Before installation of LZW4C, your C compiler should already be
installed on your system and tested. If you are not familiar with
makefiles, refer to your compiler manual. If you are using the
interactive environment for Quick C or Turbo C, be sure to compile
with the memory model corresponding to the LZW4C library used.
(2) Make a backup copy of your distribution disk. Put your
original distribution disk in a safe place.
(3) Create a work directory on your work disk (normally your
harddisk). For example, to create a work directory named LZW4C, we
first log onto the work disk and then type:
MKDIR LZW4C
(4) Copy all the files from your backup copy of the distribution
disk to your work directory. For example, to copy from the A:
drive to your work directory, we type:
CD LZW4C
COPY A:*.*
(5) Compile COMPRESS.C, EXPAND.C, TEST_LZW.C and link with the
appropriate LZW4C library (they use the COMPACT library except for
MIX Power C). For example, to make COMPRESS.EXE:
a) Borland Turbo C: Type
MAKE -FCOMPRESS._T_
b) Microsoft C: Type
MAKE COMPRESS._M_
c) MIX Power C: Type (LARGE model only)
X_COMPRESS
LZW4C Users Manual Page 5
2.0 The LZW Algorithm
The following discussion of the LZW algorithm is meant to provide
a high level overview of LZW. For those interested in a more
detailed explanation, several good books are available on data
compression.
The original research papers on what is now called LZW compression
are:
J. ZIV and A. Lempel,
"A Universal Algorithm for Sequential Data Compression",
IEEE Transactions on Information Theory, May 1977.
Terry Welch,
"A Technique for High-Performance Data Compression",
Computer, June 1984.
2.1 LZW Compression
The LZW compressor reads 8-bit bytes from a data source and
outputs N-bit codes each of which identifies a previously defined
string. The value of N starts at 9. Thus, codes 0 through 255
(0xff) correspond with the standard character set, while codes 256
(0x100) through 511 (0x1ff) correspond to a byte-byte pair or a
code-byte pair in the code table. After code 511 is output, 10 bit
codes are used. This is repeated until the maximum number of bits
per code is reached (14 in the LZW4C library).
The LZW compressor builds a code table as it compresses data. The
code table consists of previously encountered strings.
The basic LZW compression algorithm is as follows:
STRING = get first input byte
while there is more input data
{BYTE = get next input byte
if STRING+BYTE is in code table
STRING=STRING+BYTE
else
{output code for STRING
add STRING+BYTE to code table
STRING = BYTE
}
}
output the code for STRING
LZW4C Users Manual Page 6
2.2 LZW Expansion
The LZW expansion routine reads the N-bit codes previously created
by the LZW compressor and reconstructs the code table (as
previously constructed by the compressor) as it is outputing 8-bit
bytes. A code corresponds to a single byte (the first 256 codes
from 0x00 through 0xff), or a byte-byte pair in the code table, or
a code-byte pair in the code table. In the later case, the code
part of the code-byte pair refers to another defined code pair in
the table. As each code is read in, it is located in the code
table and the corresponding 8-bit bytes are output. This means
that codes must be defined before they are needed for expansion.
Unlike older dictionary based compression schemes, the code
dictionary produced by the compressor routine does not have to be
provided to the expansion routine.
The basic LZW de-compression algorithm is as follows:
OLDCODE = input first code
output OLDCODE
while there is more input data
{NEWCODE = get next input code
STRING = translation of NEWCODE
output STRING
BYTE = 1st byte of STRING
add OLDCODE+BYTE to the code table
OLDCODE = NEWCODE
}
2.3 Implementation
The LZW4C library is written in assembly language. Any Microsoft
or compatible assembler will assemble it. The decision to program
LZW4C in assembler was made in order to get the absolute maximum
performance possible. Although optimized C is very good, it is
still bigger and slower than hand optimized assembler.
The LZW algorithm requires more temporary working data space than
is available in the SMALL or MEDIUM memory models. Therefore,
there are no SMALL or MEDIUM memory model libraries provided, but
there are COMPACT (lzw4c_c.lib) and LARGE (lzw4c_l.lib) memory
model libraries.
Use the COMPACT memory model when your code will fit into 64KB or
less, otherwise you must use the LARGE memory model. Refer to your
compiler manual for a complete discussion of memory models.
LZW4C Users Manual Page 7
3.0 Example Programs
Five example programs are provided. Each example program should
be compiled with the provided makefile. These example programs
are meant to demonstrate various ways in which the LZW compression
library can be used.
If you are using an integrated compiler environment instead of
makefiles, notice that each program is compiled with the COMPACT
memory model.
3.1 COMPRESS
The program COMPRESS is provided as both a standalone LZW
compression program, and as an example of how to use the LZW4C
library to compress a file. In order to run COMPRESS, type
COMPRESS <infile> <outfile>
For example, to compress LZW4C.DOC to LZW4C.LZW, type
COMPRESS LZW4C.DOC LZW4C.LZW
3.2 EXPAND
The program EXPAND is provided as both a standalone LZW
de-compression program, and as an example of how to use the LZW4C
library to de-compress a file. In order to run EXPAND, type
EXPAND <infile> <outfile>
For example, to de-compress LZW4C.LZW to LZW4C.DOC, type
COMPRESS LZW4C.LZW LZW4C.DOC
Of course, you can only decompress a file that has been compressed
with COMPRESS.
LZW4C Users Manual Page 8
3.3 TEST_LZW
The program TEST_LZW is used to compress, expand, and verify one
or more files. It's purpose is for you to test the LZW4C library
on your own files. Your files are never modified. However, you
can NOT specify a file named "XXX.XXX" or "YYY.YYY" since these
files are work files used by COMPRESS and EXPAND. Compression
ratios ( compressed_size / original_size ) are printed for each
file compressed. For example, to test all files ending with a *.C
extension:
TEST_LZW *.C
After compiling TEST_LZW, run it against a large directory of
files as a test of the library.
3.4 MK_ARC
The program MK_ARC is used to create an archive file. For example,
to create an archive named C.ARF consisting of all files ending
with the extension '.C', type:
MK_ARC *.C C.ARF
3.5 UN_ARC
The program UN_ARC is used to un-archive the files archived by
MK_ARC. For example, to un-archive C.ARF, type:
UN_ARC C.ARF
Note that the UN_ARC program can be modified to provide for a
customized product installation program.
3.6 SEE_ARC
The program SEE_ARC is used to list the files in any archive file
created with MK_ARC. For example, to see the files in C.ARF:
SEE_ARC C.ARF
All example code should be compiled using the COMPACT memory model
(FAR data pointers, NEAR code pointers). You may create a LARGE
memory model version of the above five programs by re-compiling as
LARGE memory model programs.
LZW4C Users Manual Page 9
4.0 Reader & Writer Functions
Both the compression and expansion routines in the LZW4C library
use Reader and Writer functions supplied by the library caller.
They are provided as a means to give the caller complete control
over the source and destination of the data stream during
compression and expansion.
A reader function is not limited to reading from disk. It may read
from any data source as long as it returns a -1 when there is no
more data to be read. Similiarly, a writer function may write to
any data sink.
A simple example of suitable reader and writer functions which can
be used to compress and expand files on disk are as follows:
int Reader()
{
return(fgetc(FileInp));
}
int Writer(Byte)
char Byte;
{
return(fputc(Byte,FileOut));
}
where FileInp correspond to the input stream and FileOut
corresponds to the output stream:
FILE *FileInp;
FILE *FileOut;
FileInp = fopen(<input_file_name>,"rb");
FileOut = fopen(<output_file_name>,"wb");
Note that the Reader returns a -1 for an end of data condition.
Data is returned as an integer with the high byte set to 0. Thus,
the only integers can can be returned by the Reader are -1
(0xffff) and 0 (0x0000) to 255 (0x00ff).
If you remove data from a character buffer, be sure to zero out
the high order byte (AND with 0x00ff) unless you are returning a
-1 (EOF). For an example, examine the code for the Reader()
function in RW_IO.C.
LZW4C Users Manual Page 10
5.0 Library Functions
There are four functions in the LZW4C library as follows:
5.1 InitLZW
Function: Initialize library
Prototype: int InitLZW(char *(*Alloc)() );
Description: The InitLZW function is used to initialize the
library. The single argument is the function name of
a user supplied memory allocation function. Use the
standard C library function malloc() unless you wish
to use your own memory management function.
Returns: -2 : (CANNOT_ALLOCATE) -- if unable to allocate.
0 : (AOK) -- no error.
Example: /* initialize LZW4C */
char *malloc();
InitLZW(malloc);
5.2 TermLZW
Function: Terminate library
Prototype: int TermLZW(int (*Free)() );
Description: The TermLZW function is used to terminate the
library after all processing is done. The single
argument is the function name of a user supplied
memory de-allocation function. This is primarily a
way to free memory allocated by InitLZW. Use the
standard C library function free() unless you wish
to use your own memory management free function.
Returns: 0 : (AOK) -- no error.
Example: /* terminate LZW4C */
TermLZW(free);
LZW4C Users Manual Page 11
5.3 Compress
Function: Compresses a data set.
Prototype: int Compress(Reader,Writer)
int (*Reader)(); /* pointer to Reader() */
int (*Writer)(); /* pointer to Writer() */
Description: The Compress function is used to compress a data
set. The Reader function always returns the next
input byte. The Writer function consumes the next
output byte. Refer to the section on Reader/Writer
I/O.
Returns: -4 : (NOT_READY) -- Didn't call InitLZW() first.
0 : (AOK) -- No error.
Example: /* compress a file */
FILE *FileInp, *FileOut;
FileInp = fopen("LZW4C.DOC","rb");
FileOut = fopen("LZW4C.LZW","wb");
Compress(Reader,Writer);
int Reader()
{return(fgetc(FilePtr));}
int Writer(Byte)
int Byte;
{return(fputc(Byte,FilePtr));}
5.4 Expand
Function: Expands a file.
Prototype: int Expand(Reader,Writer)
int (*Reader)(); /* pointer to Reader() */
int (*Writer)(); /* pointer to Writer() */
Description: The Expand function is used to de-compress a file
previously compressed with the Compress function.
The Reader function always returns the next input
byte. The Writer function consumes the next output
byte. Refer to the section on Reader/Writer I/O.
Returns: -1 : (EXPANSION_ERROR) -- File not compressed by
the compress function.
0 : (AOK) -- No error.
Example: /* de-compress a file */
FILE *FileInp, *FileOut;
FileInp = fopen("LZW4C.DOC","rb");
FileOut = fopen("LZW4C.LZW","wb");
Expand(Reader,Writer);
LZW4C Users Manual Page 12
6.0 Error Codes
Be sure and check the return codes from each LZW4C function call.
There are only 4 error codes returned by the LZW4C library other
than 0 (no error). All error codes are negative numbers. Their
numerical values are in the LZW4C.H file.
Each error code is returned by a library function as follows:
****************************************************************
* Error Name * IntLZW * TermLZW * Compress * Expand *
****************************************************************
* EXPANSION_ERROR * No * No * No * Yes *
* CANNOT_ALLOCATE * Yes * No * No * No *
* INTERNAL_ERROR * Yes * No * No * No *
* NOT_READY * No * No * Yes * Yes *
****************************************************************
6.1 EXPANSION_ERROR
An EXPANSION_ERROR error is returned only by the Expand() library
function. It is caused by attempting to expand a file that was not
compressed by the Compress() function. Note, however, that
Expand() may expand a file that was not compressed by Compress()
without returning an EXPANSION error.
6.2 CANNOT_ALLOCATE
A CANNOT_ALLOCATE error is returned only by the InitLZW() library
function. It is caused when the Alloc() function passed to
InitLZW() returns a NULL pointer, indicating that it cannot
allocate sufficient memory.
6.3 INTERNAL_ERROR
An INTERNAL_ERROR error is returned only by the InitLZW() library
function and only in the shareware version. It is caused by
modification of the Shareware screen. You should never get this
error.
6.4 NOT_READY
A NOT_READY error is returned by the Compress() and Expand()
library functions. It is caused by calling Compress() or Expand()
without first calling InitLZW().
LZW4C Users Manual Page 13
7.0 Legal Issues
7.1 Registration
The shareware version of LZW4C is provided so that you may
personally determine the usefulness of the product for yourself.
If you can use the LZW4C Data Compression Library, please register
your use with us. Send $35 plus $3 S&H ($6 outside of North
America) to:
MarshallSoft Computing, Inc.
Post Office Box 4543
Huntsville AL 35815
We accept American Express (account number, expiration date,
exact name on your card, and AmEx billing address required),
checks in US dollars drawn on a US bank, purchase orders (POs)
from recognized US schools and companies listed in Dun &
Bradstreet, and COD (street address and phone number required)
within the USA (plus a $3 COD charge). Print the file PCL4C.INV
if an invoice is needed. The registered package is mailed first
class US Mail (packet air mail overseas).
Print the file LZW4C.INV if an invoice is needed. The registered
package is mailed first class US Mail (packet air mail overseas).
The registered package includes:
o No shareware screen.
o Assembler source code for the library.
o Laser printed Users Manual.
o Telephone / FAX / BBS support for one year.
o One year subscription (quarterly) to MSC newsletter.
(requires extra $5 postage if overseas)
o All updates (with printed manuals) are $15 plus $3 S&H
($6 outside of North America).
LZW4C.ASM is the source code for the library. The source code is
copyrighted by MarshallSoft Computing, Inc. The user is granted a
license to use the LZW4C object code in his own application only.
LZW4C.ASM is not shareware and may not be sold or given away to
anyone.
The registered user will receive the latest version of LZW4C by
return mail. A 5.25" diskette is provided unless a 3.5" diskette
is requested.
LZW4C Users Manual Page 14
7.2 License
MarshallSoft Computing, Inc. grants the registered user of LZW4C
the right to use the LZW4C library (in object form) in the
development of any software product without any royalties.
However, the source code for the library may not be released in
whole or in part.
7.3 Warranty
MARSHALLSOFT COMPUTING, INC. DISCLAIMS ALL WARRANTIES RELATING TO
THIS SOFTWARE, WHETHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE, AND ALL SUCH WARRANTIES ARE EXPRESSLY
AND SPECIFICALLY DISCLAIMED. NEITHER MARSHALLSOFT COMPUTING, INC.
NOR ANYONE ELSE WHO HAS BEEN INVOLVED IN THE CREATION, PRODUCTION,
OR DELIVERY OF THIS SOFTWARE SHALL BE LIABLE FOR ANY INDIRECT,
CONSEQUENTIAL, OR INCIDENTAL DAMAGES ARISING OUT OF THE USE OR
INABILITY TO USE SUCH SOFTWARE EVEN IF MARSHALLSOFT COMPUTING,
INC. HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES OR
CLAIMS. IN NO EVENT SHALL MARSHALLSOFT COMPUTING, INC.'S LIABILITY
FOR ANY SUCH DAMAGES EVER EXCEED THE PRICE PAID FOR THE LICENSE TO
USE THE SOFTWARE, REGARDLESS OF THE FORM OF THE CLAIM. THE PERSON
USING THE SOFTWARE BEARS ALL RISK AS TO THE QUALITY AND
PERFORMANCE OF THE SOFTWARE.
Some states do not allow the exclusion of the limit of liability
for consequential or incidental damages, so the above limitation
may not apply to you.
This agreement shall be governed by the laws of the State of
Alabama and shall inure to the benefit of Marshallsoft Computing,
Inc. and any successors, administrators, heirs and assigns. Any
action or proceeding brought by either party against the other
arising out of or related to this agreement shall be brought only
in a STATE or FEDERAL COURT of competent jurisdiction located in
Madison County, Alabama. The parties hereby consent to in personam
jurisdiction of said courts.
8.0 Revision History
Version 1.0 -- October 8, 1992 -- original release.
Version 1.1 -- November 11, 1992
o Added MK_ARC and UN_ARC example programs.
Version 1.2 -- March 1, 1993
o Added SEE_ARC example program.
o Minor speed improvements.
LZW4C Users Manual Page 15
9.0 Other MarshallSoft Computing Products for C
Shareware versions of all MarshallSoft Computing products are
available on our user support BBS 205-880-9748.
9.1 The Personal Communications Library for C
The Personal Communications Library for the C Language (PCL4C) is
an asynchronous communications library designed for experienced
software developers programming in C. Four compilers are
supported: Microsoft Optimizing C, Microsoft Quick C, Borland
Turbo C, and MIX Power C. An IBM PC/XT/AT or compatible is
required. The PCL features:
o SMALL, COMPACT, MEDIUM & LARGE memory models.
o 32 communications and support functions.
o Support for the high performance INS16550 UART.
o Supports hardware (RTS/CTS) flow control.
o Interrupt driven receiver.
o Supports 300 baud to 115,200 baud.
o Supports COM1, COM2, COM3, and COM4.
o Adjustable receive queues from 8 bytes to 32 KB.
o Control-BREAK error exit.
o 17 communications error conditions trapped.
o Allows 4 ports to run concurrently.
o Complete modem control & status.
o Written in assembly language for small size & high speed.
o Terminal program featuring XMODEM, YMODEM, & YMODEM-G.
The Personal Communications Library for C (PCL4C) is available for
$55 plus $3 S&H ($6 S&H overseas). It may be ordered at the same
time as the Personal Protocol Library for $65 plus $3.50 S&H ($7
overseas).
9.2 The Personal Protocol Library for C
The Personal Protocol Library (PPL) consist of a state driven
library which implements the XMODEM, XMODEM-CRC, XMODEM-1K,
XMODEM-G, YMODEM, and YMODEM-G file transfer protocols. This
allows the programmer to run multiple protocol transfers
simultaneously while interacting with the user at the keyboard.
The Personal Protocol Library for C (PPL4C) is available for $35
plus $3 S&H ($6 S&H overseas). Both the Communications library and
the Protocol library can be ordered together for $65.
The PPL requires the Personal Protocol Library for C (PCL4C) as
described above.
LZW4C Users Manual Page 16
