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CRC checksum in DFSORT

 
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revdpoel

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PostPosted: Wed Nov 19, 2008 1:53 am    Post subject: CRC checksum in DFSORT
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Does DFSORT has anything like this?
http://en.wikipedia.org/wiki/Cyclic_redundancy_check

with the crc checksum each record in a file gets a unique value

When you change the file and run the crc checksum again, you can see quickly which records have been changed, because there checksum is different
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Frank Yaeger

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PostPosted: Wed Nov 19, 2008 2:06 am    Post subject:
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DFSORT does not have a built-in function like that. However, DFSORT can do arithmetic so perhaps you could "roll your own" (or perhaps not).
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revdpoel

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PostPosted: Wed Nov 19, 2008 2:47 am    Post subject:
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Then you should know the algorithm inside the CRC checksum, I think Frank. Unfortunately I don't know.
I will go on searching
thanks
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dick scherrer

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PostPosted: Wed Nov 19, 2008 2:59 am    Post subject:
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Hello,

Quote:
Then you should know the algorithm inside the CRC checksum, I think Frank.
That makes no sense whatsoever. . .

Why should Frank know an algorithm that is not used in his product?

Do you know what a crc is? It was typically a hardware feature. . . .

If all you want is a check-digit, you can write your own. . .
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revdpoel

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PostPosted: Wed Nov 19, 2008 4:08 am    Post subject:
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don't over-react
maybe i shhould have said: "Then I should know ... ."
Is a check digit the same?
I want to compare the file of today with yesterday and see if something is changed
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enrico-sorichetti

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PostPosted: Wed Nov 19, 2008 4:26 am    Post subject: Reply to: CRC checksum in DFSORT
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here is a link to a bit of CRC philosophy
http://www.geocities.com/SiliconValley/Pines/8659/crc.htm

the objective of a check digit is the same..
but the algorithm is quite different and does not to obey a standard
for example check digits are of the general form...
given that a number is

D1 D2 D3 .... Dn 0 < Dx < 9

the the check digit(s) is/are usually calculated by
( D1*M1 + D2*M2 + D3*M3 + ... + Dn*Mn ) MODULO M
0 < Mx < 9
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dick scherrer

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PostPosted: Wed Nov 19, 2008 8:03 am    Post subject:
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Hello,

Quote:
don't over-react
My reply wasn't/i didn't. Your reply was technically off base and appeared to be more than just a bit rude. This will often receive a similar reply.

Quote:
maybe i shhould have said: "Then I should know ... ."
Maybe, but i don't know why you should have known either icon_smile.gif After all, that is the topic you asked about icon_wink.gif
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revdpoel

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PostPosted: Thu Nov 20, 2008 3:28 am    Post subject:
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Dick,

you say : If all you want is a check-digit, you can write your own. . .

How do I write a general check-digit? If I want to compare two records of FB 80?
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dick scherrer

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PostPosted: Thu Nov 20, 2008 7:38 am    Post subject:
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Hello,

I am probably mis-understanding something, but if you have 2 sets of records that do not already have a check-digit, is there a reason to use something other than SUPERC?

If the records already have a check-digit. . . ?

As i mentioned, i am probably mis-understanding something. . .
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revdpoel

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PostPosted: Thu Nov 20, 2008 11:38 pm    Post subject:
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the records don't have a chkdigit
superc is not allowed in production
I need to know which records have been changed
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Alain Benveniste

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PostPosted: Fri Nov 21, 2008 12:18 am    Post subject:
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revdpoel,

Did you go to the "Smart DFSORT Tricks" paper at:

www.ibm.com/systems/support/storage/software/sort/mvs/tricks/

and took a look at:

Create files with matching and non-matching records

You could find your solution ...

Alain
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revdpoel

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PostPosted: Fri Nov 21, 2008 12:53 am    Post subject:
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thank you
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dick scherrer

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PostPosted: Fri Nov 21, 2008 4:33 am    Post subject:
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Hello,

FWIW, posting a requirement is usually more productive than posting a question about some potential solution for an undefined requirement.

I suspect that had the question originally been about how to compare 2 files rather than about implementing check digit/crc logic, Frank would have originally replied with something quite similar to what Alain posted.

I only mention this as it might have saved you couple of days icon_wink.gif
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Frank Yaeger

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PostPosted: Fri Nov 21, 2008 7:10 am    Post subject:
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Excellent point, Dick.

This kind of thing seems to happen quite often. Somebody gets a notion in their head about how something could be done and asks the wrong question leading to confusion and wasted time. Much better to describe the requirement in detail with examples so the "best" solution can be suggested.
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