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RE: Parise MIR KEPS



At 02:14 PM 3/11/99 -0800, Duane Naugle wrote:
>	You may have to change the check digit if you change the space to 
>a zero. 

Turns out you don't.  The check digit algorithm is really pretty dumb.
It adds in each digit as its literal value, and most other characers
(spaces, letters, punctuation, etc.) don't count.  So since "0" is
worth 0 and a space is also worth 0, no check digit change is
required.

The only exceptions are "-" and "+".  The minus sign counts as 1.
The plus sign counts as either 0 or 2, depending on who generated
the elements and when.

It doesn't notice transposition of digits, it's easy to make compensating
errors, and even if you type in random garbage the check digit will
match 10% of the time.  Very poor design.

The AMSAT format checksum (when it's used) is the same
algorithm, except you send the whole sum instead of just the
last digit.  This is still pretty dumb, but at least it won't pass
complete garbage very often.

73  -Paul
kb5mu@amsat.org


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