Why "YCRC" instead of CRC-32?

Why "YCRC" instead of CRC-32?

Postby mike-stgt » Wed Jul 13, 2022 10:14 am

For quite some time cyclic redundancy check (CRC) is a nice attempt to detect changes to digital data. Well known is the "type" CRC-32 because its widespread use by PKZIP, ZIP, 7-Zip and more. In contrast the ROMs for 41CL are listed with a "YCRC" which turns out to be "type" CRC-32/MPEG-2. This is also wide spread since used in VLC but not accessible for the average user for his own use. (BTW, I prefer the term "type", typically it's called "algorithm", but the idea behind CRC is all the same, only some parameters are varied what may result in special, maybe optimised algorithms.)

Question: Do we know any reason why Monte J. Dalrymple did not use CRC-32, so comparing ROMs would be possilbe for everybody, without an extra program?

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M.
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Re: Why "YCRC" instead of CRC-32?

Postby pcscote » Wed Jul 13, 2022 3:16 pm

mike-stgt wrote:Question: Do we know any reason why Monte J. Dalrymple did not use CRC-32, so comparing ROMs would be possible for everybody, without an extra program?

No, but you could send him an email and I am sure he will explain why.
I guess he already had an implementation for that specific crc calculation and he just decided to reused it.
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Re: Why "YCRC" instead of CRC-32?

Postby mike-stgt » Thu Jul 14, 2022 10:49 am

pcscote wrote:... but you could send him an email and I am sure he will explain why.

Yes, superb idea, but even I was nosy some days ago I'm not interested any more because a few hours ago I had to learn, there exist programs to get CRC results ad lib. In consequence you may manipulate a ROM file and (if there is some vacant space) enforce to compute the original CRC. Therefore (almost) all CRC data is of questionable usefulness.
Nonetheless Christoph shows "YCRC" in his ModEdit, my youngest mkMOD computes on request CRC-32/ISO-HDLC and CRC-32/MPEG-2 (= "YCRC"), but just for fun. IMO it is of minor importance.

/M.
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