A set of file compression and decompression programs
By Steve Emsley
C-64
File Packer 64 shortens and combines disk files just like other file-compression programs. However, unlike programs that compress multiple files into a single large one, File Packer can compress files individually or in any combination. In addition, it can encode each compressed file differently for added protection from unauthorized decompressing.
Load the program using Menu 64. File Packer's menu offers four options: Save Unpacker, Pack File(s), Append File(s), and End.
Option 1 saves to disk a one-block file called Unpacker. Choose a memory location that isn't needed for other things; 32768 and 49152 seem to work best. Then place a formatted disk in the destination drive and press any key to initiate the save.
Option 2 compacts individual files. Enter the current filename and the new filename, or press return without either entry to go back to the menu. Be sure a machine language or text file is last; if a Basic program file is last, File Packer won't work.
Next, enter a number from 0 to 255 as an XOR byte. File Packer will encrypt the file (including the load address) by exclusive "ORing" with this number. A blank entry leaves the file unencoded.
Because the exclusive OR byte is stored in the file and not the unpacking routine, each file can have a different encryption number. The files are secure from tampering because then they must be loaded with the unpacking routine.
After the file is found, File Packer displays the original load address for you to change or keep. Pressing the left-arrow key aborts to the menu (as does a disk error).
Depending on the size of the file, the encoding and crunching takes from one to several minutes. When it's done, you can go on to another file.
Unlike file compactors that require loading three or four files to compress, File Packer requires just one. Also, because the load address of each file is separate, the files can be packed in any order, provided the last file packed is not a Basic program.
Option 3 is for appending a file to an existing packed file. Enter the name of the file to be appended and the name of the packed file.
Option 4 quits the program.
File Packer redefines the following keys: S changes the source device, should you want to use a second drive (drives 8-11 are supported); F1 and F3 toggle the source (read) and destination (write) drives; F5 and F7 display directories of the source and destination disks.
You have two choices for uncompressing files. First, you can use the Unpacker routine created by File Packer, which unpacks the files only in RAM. Once you've saved it to a formatted work disk, use LOAD "UNPACKER",8,1 to load the unpacking file. To load a compressed file from disk, use OPEN 8,D,2,"0:FILENAME":SYS LOCATION, where D is the device number and SYS LOCATION is the address of the unpacking routine. The screen border flickers to let you know when the compressed file is loading and stops when it's done. The compressed files then reside in memory at the locations specified during the packing process.
The second, and easier, way to use the program is to use UNPACKER.BAS, which is written to your work disk when using the Copy option from Menu 64. Once it's on the work disk, just load and run it as follows:
LOAD "UNPACKER.BAS",8
RUN
Enter the name of the compressed file at the prompt, and the uncompressed files will be written to disk as FILE A, FILE B, and so on.
The packing routine is based on repetition, so it works best with sprite files, picture files and program files created by word processors. The program and its accompanying files are rather technical in nature, requiring careful use in order to operate them correctly. If you have trouble unpacking files, repack them using different addresses or in a different order.
