The name:
 
   DMPATCH.EXE

The purpose:

   To allow simple, consistent ways to patch the DOOM executable.

The program:

   This is a very simple patch program.  It was written with DOOM in
   mind, but should be able to be used with almost any file (with some
   things in mind, see caveats).  I wrote it to be flexible, and made
   it allow easy patches to different versions of the executable.

   This program takes either 1 or 2 command line arguments.  If there
   are two command line arguments, the first is the name of the file,
   and the second is the offset in the file to make the modifications.  
   If there is only one argument, it is the offset into the file.  In
   this case, the file 'doom.exe' in the current directory is assumed
   to be the file to edit.

   After the program starts, and it does a few things, it will ask you
   how many bytes you want to change.  Enter the amount you desire.

   Now the program will put you in a rather crude editing mode.  The
   current values at the requested address will be display, and a
   "_" will be shown a couple of lines below.  This represents the
   current editing position.  You may enter in the patch values you
   want.  If you make a mistake, the backspace should work; however,
   I wouldn't count on it 100%.  Try not to make mistakes, and don't
   start without backing up the original.

   After you have entered the correct number of bytes, the program will
   display what you entered and ask if that is OK to patch.  If you
   say yes, the program will patch the addresses and drop you out on the
   DOS command line.  Otherwise, it will just drop you out in DOS that
   much faster.

The good:

   I am trying to get a consistent way to publish the many things I
   have found about the executable in a way that will help most people.
   I will organize this into some sort of table ASAP.  I am always 
   welcome to new entries from anyone, and will also field requests
   to figure out patches to do new things.

The bad:

   This program will modify your executable.  If you enter erroneous
   information, you could DESTROY your executable.  Please backup the
   DOOM.EXE (or whatever other file you are patching) before beginning.
   I have tried to make sure it is stable, but we all know how that
   goes.  If anyone catches anything I missed (bugs that is), I would
   appreciate a line.

The ugly:

   MY INTERFACE.

   This program is crude.  It is not user friendly.  I did not spend a
   lot of time on it.  If you have suggestions for interface or other
   modifications/additions, I would love to hear them (particularly if
   they are not too complex to implement).

The example:

   Say I want to change 4 bytes at hex offset 8ab48 in doom.exe (which is in 
   the current directory)

     dmpatch 8ab48

     Then enter 4 when it asks how many bytes to change, etc, etc.

   Say I want to change 6 bytes at hex offset 12af9 in \games\doom\doom.exe
   (which is NOT in the current directory)

     dmpatch \games\doom\doom.exe 12af9

     Then enter 6 when it asks how many bytes to change, etc, etc.

The caveats:

   I wrote this for my own use.  For this reason, I wrote it to be
   most compatible with the disassembler I use.  The disassembler that
   I use does some weird segmenting stuff with the DOS4GW header, and
   hence, subtracts 1dd0 (hex) from each address (ie: offset 5dd0 in the
   file appears as 4000).  So, the patch values that I supply will be
   1dd0 (hex) less than their actual offset in the file.  If you are
   going to use this program on a file other than DOOM, keep this in mind.

The request:

   I would love to have some help disassembling doom.exe.  If anyone has
   done any of this and would like to share it with me, I will add it
   to what I have already (and of course give credit where due).  I think
   we could get a pretty decent list pretty quick with a few peoples
   input.

The BS:

   I wrote this program for my own use.  I am releasing it into public
   domain so that others can use it to.  I make no guarantees express
   or otherwise about its operation.  If you can't deal with that, don't
   use it.  I will not accept responsibility for how this program is
   used (particularly if it is illegal), or what it does to your 
   information if you use it wrong or there is a bug in it.  The program
   may be freely distributed.

   ID software has no knowledge (to my knowledge) of this software and
   is in no way affiliated with it.  They cannot be held responsible for
   it in any way.

Please any suggestions/observations/etc e-mail to me.

Steve Larsen
larsen@sunset.cs.utah.edu
larsen@unislc.slc.unisys.com