This package contains "DisFilter", a disassembling binary x86 code
preprocessor that increases compressability by LZ-based compressors
or context coders. It was originally developed for my Win32 executable
compressor kkrunchy. I've been planning to release this publicly for
several years now, but the code was the result of intensive experimentation
and looked the part; I didn't want to give it to anyone without at least
cleaning it up first.

When using LZMA as compression backend, DisFiltered executables are
typically about 10% smaller than executables preprocessed with the default
LZMA filters (call transform), and about 20% smaller than unpreprocessed
files. This result seems to be quite robust among my (admittedly small)
test set containing a few large Windows executables/DLLs (among others,
photoshop.exe from Photoshop 7.0, thunderbird.exe from Mozilla Thunderbird
2.0.0.23, and xul.dll from Firefox 3.5.5; just a sample of large
executables I found on my harddisk). The transformation is completely
reversible - in the worst case, the result will compress notably worse
than the original data.

The algorithm is described at the top of the main source file, "dis.cpp".
The code should be fairly straightforward from there; the main source of
complexity is the x86 instruction encoding itself. I've also included a
small demo application (main.cpp) to show how it is intended to be used.
The code was written using Visual C++ and the demo application reads
PE files, but nothing about it really is Windows-specific; it should work
equally well for Linux or other OSes.

The code doesn't handle the newer 3-byte opcodes, and it doesn't understand
x64 code. Both of this should be relatively simple to add; I simply had no
use for this myself so far.

I hereby place this code in the public domain. I'd be happy if other
contributors do the same with their changes. I can provide no warranties or
other guarantees about this code or files generated by it. I've tried to
be careful though :)

Feel free to contact me with any questions or suggestions.

- Fabian "ryg" Giesen, November 2009
  ryg@gmx.net