RE: Generate hash code for a source member?

Dan:

First thing to keep in mind is that no hash value is going to be
foolproof unless your hashes have as many significant characters
as your largest members. Hashes can be pretty good, but they
won't guarantee uniqueness.

With that in mind, note that _most_ switched characters will
indeed generate different hashes; the XFOOT was suggested over
groups of 4 characters for 32 bits. "ABCD" is definitely a
different 32-bit value from "BACD", e.g., 3250766788 vs.
3267478468. Similarly, "ABCD" and "EFGH" are together different
from "ABCE" and "DFGH". That is, while many transpositions won't
be caught, most of them will be caught.

Switched records are slightly more trouble, but something such as
RRN being used a kind of seed value should help.

The real question comes down to exactly how precise do you need
this to be? Do you need to guarantee you'll catch every
duplication or variation?

Tom Liotta

"Dan Bale" wrote

> A simple XFOOT solution, I'm thinking, will not catch changes
where
> characters are switched, or where records are switched.  I
realize I could
> introduce some logic to multiply each element in a record by a
different
> value, and do something similar by RRN, and then have to deal
with overflow,

--
Tom Liotta
The PowerTech Group, Inc.
19426 68th Avenue South
Kent, WA 98032
Phone  253-872-7788
Fax  253-872-7904
http://www.400Security.com
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