AVR-Chat

On Thu, Jun 17, 2010 at 05:22:42PM +0200, Marc R.J. Brevoort wrote:
> On Sun, 13 Jun 2010, Jim Wagner wrote:
> 
> >> could it be a byte order problem in the computed CRC or the
> >> polynomial?
> 
> This thread has been active for a while now. Although CRC is a
> superior checksum scheme, considering the effort this seems to be, I
> was curious why you specifically want a CRC checksum, as opposed to a
> simpler checksum scheme?

I haven't been in this thread, but have traveled this road. Very often
a number claimed to be a CRC is generated by an outside source that one
has no control over. Therefore one has to go about trying to find an
algorithm to reproduce the same results.

No matter one supposedly knows the polynomial, not everyone applies it
the same. Some start the summing with zero, others with -1.

At least one school of thought believes the last N bits shifted into a
CRC-N polynomial are not fully represented. Their solution is to "close"
the calculation by feeding a known value such as -1 (N bits in size)
in to the CRC. Once this is done one can not append more data, hence its
a closing act.

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
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Whom computers would destroy, they must first drive mad.