This is a simple runlength packer for data in Pascal/Delphi. It was used a lot in DOS to save valuable memory when storing data on disk or inside of a program. Data that has many repeating characters can be compressed well. This is often useful for graphics, palettes, levels and other data used in games.

Use pack.exe to compress a file:

pack input-file output-file

As a very simple example, suppose you have a file level1.txt that represents a level for a game

XXXXXXXXXXXXXXX
Xsx.....x.....X
X.xxxxx.x.x.x.X
X...x.x.....x.X
Xxx.x.xxxx.xx.X
X...x......x.fX
XXXXXXXXXXXXXXX

Pack it with the command: pack level1.txt level1.pck

Old size: 119  New size: 79  Gain: 40 (33.6%)

The new (binary) file now looks something like this:

OX�.XsxE.�xE.�X.X.Exc.x�.X.XÃ..xx..xX�.XBxb.xCx�.Bx�.X.XC.�xF.�x.fX.OX�

The program bin2pas provides an easy way to get your packed file (or basically any file) right into your Pascal/Delphi code. It has the same syntax as pack:

bin2pas input-file output-file

So in this example, we can run: bin2pas level1.pck level1.inc

This produces a new file level1.inc, which has the following contents:

procedure level1pck; assembler;
asm
  db  79, 88,  5, 13, 10, 88,115,120, 69, 46,  1,120, 69, 46,  5, 88
  db  13, 10, 88, 46, 69,120, 99, 46,120,  5, 46, 88, 13, 10, 88,199
  db  46, 46,120,120, 46, 46,120, 88,  3, 13, 10, 88, 66,120, 98, 46
  db 120, 67,120,  1, 46, 66,120,  5, 46, 88, 13, 10, 88, 67, 46,  1
  db 120, 70, 46,  6,120, 46,102, 88, 13, 10, 79, 88,  2, 13, 10
end;

You can include this file into your Pascal/Delphi code using the directive

{$I level1.inc}

To reference the data, you can use @level1pck (as a pointer) or @level1pck^ (the actual data).

In your Pascal or Delphi code, you can include the code to unpack your data by using the directive

{$I UNPACK.INC}

It contains two functions:

• procedure Unpack(p: Pointer)
• function GetNextByte(): Byte

In your code, start by calling unpack once and then use GetNextByte to get each next (uncompressed) byte of data. Note: You need to know the size of your data or have a way to recognize the end of the stream.

So in our example, you could have something like:

Unpack(@level1pck);
for j := 0 to LEVEL_SIZE_Y - 1 do
  for i := 0 to LEVEL_SIZE_X - 1 do
    case Chr(GetNextByte()) of
      'X': ...

Of course, this example is way too small for this to be beneficial. However, this system was used successfully in most games by Wiering Software, at least the ones written in Pascal/Delphi.