Re: Patterns.

James Courtier-Dutton wrote:
> Hi,
> 
> I have been doing reverse engineering for some time now. I think it 
> would be good to start building up a web site with a list of patterns.
> e.g.
> If you see this group of assembly instructions, then this is the concept 
> they are implementing.
> I think this would be particularly useful for reverse engineering codecs.
> For example, we could describe a concept, like for example IDCT, and 
> then list each of the different ways it has been implemented in actual 
> code.
> Then, when a new looking IDCT routine is discovered in some binary code, 
> it will be added to the list.
> 
> Then people reverse engineering code, could much more easily get back to 
> the concept behind the binary instructions, and then document the 
> conceptual algorithm for the code, so that other people could then 
> implement it.
> 
> I am currently working on a project that will display binary code in a 
> more readable form than assembly instructions. The aim is to display it 
> as a code snippet in C. I fully understand that it will not be perfect, 
> but I feel sure that it will at least speed up the task of reverse 
> engineering assembly code.

	Good idea, and I encourage you to keep it up. For my part, I am still 
trying to write a series of articles about core video coding concepts in 
plain, non-mathematical English:

   http://multimedia.cx/eggs/index.php?cat=16

The reason for this is that I realized that there are a lot of REs out 
there who want to delve into binary codec code but do not understand 
what they might find. That's why I wanted to describe what the 
algorithms most commonly look like.

	It has been a little slow going. Here are the current articles:

* RLE
* Differential Coding
* Mean Removal
* (Scalar) Quantization
* Frame Types

The articles I have in the queue include:

* YUV and RGB Colorspaces And Pixel Formats
* Building Blocks (discussing basic decoding flow)
* The Magical Discrete Cosine Transform
* Motion Compensation
* Vector Quantization
* Huffman Codes/Variable Length Codes
* Machine Optimizations

I know wavelets should be on there as well. But I know less about those 
than I do about DCT.

-- 
	-Mike Melanson


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