This program will generate a valid digital signature for an Atari 7800
cartridge ROM image.

The code was created by hand-decompiling the original 7800 encryption
program for the Atari ST into plain C code, so it does not rely on any
external libraries and should compile for almost any operating system
with no muss and no fuss.


To run it:
==========

   sign7800 -t filename   to test for a valid existing signature only
   sign7800 filename      to generate a signature printed to stdout
   sign7800 -w filename   to generate a signature and update the image

'Filename' is the name of the file with the cartridge data in it.  It
must be a binary file, with a size that is a multiple of 4K bytes.  An
extra 128 bytes is allowed, so that you can use it with a .A78 file.

The '-t' option only tests to see if an existing signature is valid.

The '-w' option causes the file to be updated with a new signature if
it was not aready valid.  A write will not happen if there is a problem
with $FFF8, $FFF9, or the reset vector, or if there is already a valid
signature in the file.  Even with an already valid signature, a new
signature is still computed and printed to stdout.

WARNING:  using the '-w' option should be safe if your file is really a 7800
cartridge image, but if it isn't, there is a possibility that data loss
to the last 128 bytes of the file could occur!  Be sure that you have a
backup copy of or can re-create whatever file you use with the '-w' option!

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                 8520   14828  57.5% -lh5- f318 Jun 23  2004 sign7800
[generic]                 5797   17177  33.7% -lh5- 2965 Jun 20  2004 sign7800.c
[generic]                  855    1764  48.5% -lh5- 1eb9 Jun 23  2004 sign7800.readme
[generic]                 1939    4523  42.9% -lh5- a066 Jun 20  2004 sign7800.txt
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total         4 files   17111   38292  44.7%            Jun 27  2004