Re: Interesting code I need help with

From: Ojala Pasi 'Albert' (albert_at_cs.tut.fi)
Date: 2004-04-15 12:11:01

> I see now the algorithm, but can;t seem to grok the a001

The a001 defines the feedback for the delay line.
The way to represent the CRC would be something like:
          _________________________________
         |   __      __  |   __        __  |   __
         |  |  |    |  | |  |  |      |  | |  |  |
Din >--X-+->|D |--->|D |-X->|D |- .. >|D |-X->|D |->.
       |    |__|    |__|    |__|      |__|    |__|  |
       |    8000    4000    2000      0002    0001  |
       |____________________________________________|

Where X depicts XOR and + is just a connection. The constant
0xa001 defines the feedback connections.

> CRC code must only generate a 16 bit number with the low bit of both 
> bytes off.  So XXXXXXX0YYYYYYY0.  Very strange.

Should not be. Maybe you are misunderstanding something in the code?

-Pasi
-- 
/Light, she loved Elayne almost as much as Rand - maybe as much, in a
 very different way - but how was a woman to compete with a beautiful
 golden-haired queen who had a powerful nation at her back and call?/
	-- Min in The Wheel of Time:"The Path of Daggers"

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