Re: Fletcher Checksum Question

From: CBFalconer (cbfalconer@yahoo.com)
Date: 02/04/03 

From: CBFalconer <cbfalconer@yahoo.com>
Date: Tue, 04 Feb 2003 20:33:31 GMT

Stephen Ymage wrote:
>
... snip ...
>
> ignoring the "&" operation, the function is:
> s1 = s1 + data;
> s2 = s1 + s2;
>
> lets call the data values: a1, a2, a3, a4,...
>
> at iteration 0:
> s1 = 0
> s2 = 0
>
> after iteration 1:
> s1 = a1
> s2 = a1
>
> after iteration 2:
> s1 = a1 + a2
> s2 = a1 + (a1 + a2)
>
> after iteration 3:
> s1 = a1 + a2 + a3
> s2 = a1 + (a1 + a2) + (a1 + a2 + a3)
>
> after iteration 4:
> s1 = a1 + a2 + a3 + a4
> s2 = a1 + (a1 + a2) + (a1 + a2 + a3) + (a1 + a2 + a3 + a4)

After all this fooferaw someone finally explained what that
checksum is (I think). What is it used for? If for such things
as creating checkdigits for numeric entry, it is flawed because it
will systematically drop high order bits from later digits. 

-- 
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
   <http://cbfalconer.home.att.net>  USE worldnet address!

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