Hi, Rod.

RS> PE> Now what you see here is that the compressed sizes are different!!!
RS> PE> If it was a disk read error (or disk cache read error), it would
RS> PE> have created a different CRC, because the data would be different.

RS> FM> I don't know which ZIP you use (I use PIP 2.04g) but I have seen this.
RS> FM> It depends what zip finds in the way of operating system, hardware,
RS> etc.
RS> FM> eg if it finds a more competent processor it will use the appropriate
RS> FM> instructions. In your case it's probably found a different amount of
RS> FM> memory, enabling it to build a bigger table when it could.

RS> RS> Cant be that, doesnt explain the SAME CRC in the two files.
RS> RS> THAT indicates that whatever is doing the CRC sees all the
RS> RS> data fine, but it doesnt all get into the file created.

RS> FM> The 2 files were the *same* file.

RS> The same INPUT file, sure, clearly not the same OUTPUT file tho,
RS> the length was different. So the CRC should be different too.

No. The CRC of a file within an archive is calculated on the data in the
original file, not the compressed file, for all of the following: ARC,
ARJ, LHARC, PAK, PKZIP, SQZ, ZOO and any compatible programs.

RS> FM> As I read the description the change from $00 to $20 was a completely
RS> FM> separate problem, which nevertheless managed to confuse the situation.

RS> What was being discussed is if repeated rezipping of the SAME file
RS> can produce DIFFERENT zip files, different lengths, but with the
RS> SAME CRC. Its quite easy to see how repeated rezipping can produce
RS> a differently compressed file, most obviously with a different set of
RS> dictionary terms, but that WONT produce two files with the SAME CRC.

Yes it will. See above.

RS> RS> Let alone produce the result where using the dud file gets a
RS> RS> complaint about the CRC coz the file has some missing bytes.

RS> FM> I don't think that's what happened. That's not how I read it.

RS> Thats what he said quite specifically. I did truncate
RS> that quote back a long way from the original full text.

No.

RS> FM> In my example, the exact same file zipped using the
RS> FM> exact same program on my machine here cf the one at work,
RS> FM> gave different file sizes (it usually does in fact).

RS> RS> Sure, different say ram available could well produce that
RS> RS> result, BUT that is very unlikely to produce the SAME CRC.

RS> FM> From the same data it will, and that's what I think was
RS> FM> happening. The one byte change was a different problem.

RS> Nope.

Yes.

Regards, fIM.

 * * It's great to do nothing and rest afterwards.
@EOT:

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