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Wilbert van Leijen
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PACKOBJ.DOC  --  The Turbo Pascal Compressing Data Objitizer

                        By Wilbert van Leijen


PACKOBJ is a program that takes binary data as input, compresses it using a fast LZW algorithm and converts it to an .OBJ file that you can link in a Turbo Pascal (TP) program, version 4.0 or later. TPUNPACK.PAS is the TP unit that takes care of decompressing the data.

The PACKOBJ.EXE program and the Turbo Pascal TPUNPACK unit are distributed as Shareware. If you use them, you are kindly asked to register this product. The fee for becoming a Registered User of PACKOBJ/TPUNPACK is $15.-- or $25. (that's twentyfive Dutch guilders). Just send a cheque or money order to the author. My address is mentioned at the bottom of this document.

Upon registration, you will become a disk with:

  • the source code of the PACKOBJ utility and UNPACK routine
  • 3 different customised TP 6.0 Runtime libraries (SYSTEM.TPU):
    one 'Regular Version': 100% compatible with Borland's, but with many code enhancements and improved 'smart linking'; one 'Regular 286 Version', with 286 code throughout, aborts automatically when an attempt is made to run a program on an XT-class system; and one 'STUB Version', designed especially for crafting ultra compact utilities and TSR programs.

The STUB version of SYSTEM.TPU was used to compile PACKOBJ. STUB is a limited version of the runtime library in the following respects: it does not support overlays and virtual methods; it doesn't automatically open/close the text files Input and Output (they are pre-declared, however); it doesn't take over any interrupts; and it passes control to DOS to do the allocation and deallocation of data structures on the heap. STUB will be accompanied with guidelines for developers. As a rule, if you're not deeply into object oriented programming, the majority of your TP programs will benefit from STUB. Example: the minimum .EXE size of a program created with STUB ('begin end.') is only 224 bytes.


PACKOBJ's command line is akin to BINOBJ, a utility shipped with every version of Turbo Pascal since 4.0. BINOBJ expects you to specify an input file, an output file and an exported identifier. PACKOBJ wants you to tell it:

  • the name of the input file; this file can be of any type, whether it is an ASCII document, a picture bitmap or whatever. The only limitation here is that it must be smaller than 64 kByte;
  • the name of the output file; this will hold the compressed result and is linkable in a TP program;
  • an exported identifier or 'public name': this is the symbol that must be specified in order to link the .OBJ file in your TP program.

Unlike BINOBJ, the PACKOBJ utility will declare not one but two public names. And unlike BINOBJ too, these two public names are callable by your program, i.e. you don't have to pass a pointer to it to access your data.

The public names exported by PACKOBJ are of the format:

   Funtion PublicNameSIZE : Integer; Far; External;
   Procedure UNPACKPublicName(Var buffer); Far; External;

The PublicNameSIZE will return the size of the unpacked image. This is handy if you want to know how many bytes you'll have to allocate on the heap to hold the result in 'buffer'.

UNPACKPublicName does not do any unpacking. Rather, it pushes a few parameters on the stack and performs a far call to UNPACK. UNPACK is the interfaced procedure of unit TPUNPACK.

Note that you must attach the pseudo-type 'Far' to the declaration in your declaration or alternatively, enable the compiler directive {$F+ }.
Failure to do so will most likely crash your program or the entire system.

Sample usage:

   PACKOBJ joltcola.PIC joltcola JoltCola

This will take JOLTCOLA.PIC as input, writes JOLTCOLA.OBJ as output. It will declare the procedure 'UNPACKJoltCola' and function 'JoltColaSIZE' public.

Suppose you have JOLTCOLA.PIC. This is the raw bitmap of a VGA mode 13h picture of a cola brand, loved by weary programmers because it promises 'Twice the Caffeine'. The picture is 64 kByte big, but we can put the squeeze on this.

In this case, JoltColaSIZE returns the size of the raw, uncompressed bitmap: 65520 bytes. For a straight dump of the picture to the VGA display however, calling JoltColaSIZE is not needed: the VGA memory is already there, and unaccessible by TP's heap manager anyway.


UNPACKJoltCola calls a Far routine by the name of UNPACK. This routine is exported by unit TPUNPACK and it takes care of the actual decompression of the information. TPUNPACK is entirely written in assembler and optimised for speed. Hence, it uses no more than a mere 474 bytes of code space.

Please note that UNPACK's stack requirements are somewhat less modest. You must reserve 29 kByte of stack space to allow room for UNPACK's work space.

The deal is here that you must include 'uses TpUnpack' under the program header of your TP application and, specify a memory allocation directive to allow for 32 kByte or more of stack space. Example:

   {$M 32768, 0, 0 }           { Allocate 32k stack space, no heap }

Do not call UNPACK by your application -- unless you know exactly what you're doing. UNPACK will be called by the loader code of any .OBJ file created by PACKOBJ.

Running the demo

In order to compile and run the demo, you must have the following:

  • Turbo Pascal, version 4.0 or later
  • A VGA display. (Any VGA display will do.)

What you must do:

  • Make TPC.EXE, the Turbo Pascal command line compiler, accessible on the DOS path

Trade Marks

Turbo Pascal is Copyrighted by Borland International. PACKOBJ and TPUNPACK are Copyright 1991-92 by Wilbert van Leijen, Amsterdam, The Netherlands.


Wilbert van Leijen
Marathonweg 72-2
NL-1076 TM Amsterdam
The Netherlands

Wilbert van.Leijen at Fidonet 2:500/12.10956