Humm... My Brain Hurts.. You crazy optimising people are giving me a
headache trying to keep up :)

If you are interested, a full discussion about how CRCs work is presented=
 at
http://www.geocities.com/SiliconValley/Pines/8659/crc.htm

This is what I based my original code on.

I was trying to produce a _simple_ and relatively small CRC routine and I
seem to have been out-done in a big way.. Oh well :)

Maybe I should have a look at this again in the morning when I've drunk l=
ess
beer.. :P Might make more sense.

Cheers,
Ash.

---
Ashley Roll
Digital Nemesis Pty Ltd
www.digitalnemesis.com
Mobile: +61 (0)417 705 718




> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of K=FCbek Tony
> Sent: Tuesday, 14 May 2002 8:54 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: Small Table Driven CRC16 Routine
>
>
> Hi Scott and Ashley,
> nice initiative and somewhat challenging :) *gee* probably to
> much free time
> today. Anyway I concluded by reading the original post the
> same result as
> Scott
> did, there were ways one could skip the table and make some
> parts shorter.
> However
> one thing was still bugging me, the double 4 bits shifts, I
> felt that these
> should not be
> needed. Wrapping my head around what exactely was happening (
> I never have
> dealt with CRC
> or feedback registers before ) made me realise something,
> kind of an 'aha'
> experience,
> so without further ramblings here goes an *really breifly*
> commented version
> ( for challenge ).
> It works with the test vector but don't take it for granted
> that it's fully
> operational :)
> ( although I think so ).
>
> It does not save much in regards to Scotts version
> (unrolled), but I guess
> it is atleast
> a few cycles shorther.
>
> Ofcource I'll post an more commented version if there is
> anyone who actually
> is interested,
>
> The snippet is really migrane inducing :) and not for the
> faint hearted.
>
> I needed three temps, and used the 'available' in the
> original snippet.
> Executes in around 36 instr./byte, no additional stack or
> tables are needed
> (including call/return).
>
> But it wouldn't surprise me if Scott,Nikolai or Bob presents
> an 10 cycle
> version :) *hint* hint*
>

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