Disasm 1.0.0
============
Copyright (c) 1999 Marius Gedminas <marius@gedmin.as>
This program is Free Software.  See file COPYING for details.

It is a small disassembler for Intel 8086 and 8088 processors.  It can only
read .COM files not bigger than 60 Kb (61440 bytes).  Newer processors are
not supported; the 8087 coprocessor instructions are not supported either.

The output file is a standard .ASM file that should compile with TASM or
MASM.  Only TASM version 3.2 was tested.  The file reassembled from this
source may differ from the original executable, especially, if the latter
one was originally assembled with a different assembler.  This is due to the
fact that many assembler instructions can be encoded in different but
semantically equivalent ways.

The purpose of this program is to help me avoid the exam in Computer
Architecture.  It was also an interesting exercise.

Disasm was developed with TASM 3.2.  It will not assemble with MASM, as it
uses TASM's IDEAL mode.  The code was written using the VIM text editor
under Red Hat Linux and debugged with the help of DOSEMU.  The 8086/8088
instruction table (opcodes.dat) was created with the aid of Tech Help! 4.0a
and verified with the Info documentation from Netwide Assembler.  Note: both
sources contain errors!  Later, this table was verified directly by feeding
hex codes to Netwide Disassembler and looking at the output.  The table was
converted to .asm include file with a Perl script (opasm.pl).

First version of Disasm was written in Free Pascal.  This was done for a
couple reasons:
  * In the beginning I did not know it had to be written in assembler
  * This greatly helped me to design the assembler version; even if I
    knew from the beginning about the need to program in assembler, I
    would first create a Pascal prototype

Actually, if I tried to produce the first version already in assembler, I
would probably have failed or given up.  The Pascal version showed me this
task was not very complex (actually, it looks pretty simple now).

Note: I did not try to reverse-engineer (i.e. disassemble or inspect with a
debugger) the compiled Pascal version.  Writing assembler code is hard
enough, but inspecting disassembled code is much harder.

The Pascal version is also distributed (although it is now obsolete and
contains a couple of bugs fixed in the assembler version).


The author: Marius Gedminas <marius@gedmin.as>.

References:
* VIM -- Vi IMproved (version 5.4) by Bram Moolenaar et al.
  http://www.vim.org/

* Red Hat Linux distribution
  http://www.redhat.com/

* DOSEMU -- The DOS emulator (version 0.99.13)
  http://www.dosemu.org/

* TASM -- Turbo Assembler (version 3.2) by Borland International
  http://www.inprise.com/

* Tech Help! 4.0a by Dan Rollins, Flambeaux Software, Inc.

* NASM -- Netwide Assembler 0.98 (also contains Netwide Disassembler)
  http://www.cryogen.com/Nasm/

* Perl -- a very popular scripting language
  http://www.perl.org/
  http://www.perl.com/

* Free Pascal Compiler
  http://www.freepascal.org/

$Id: README,v 1.1 2002/10/20 18:01:10 mg Exp $