Hi, Peter.

NP>  > A CRC applies a polynomial which is calculated to minimise the
NP>  > probability of a change to the file ending up with the same CRC.

NP> I got the file that Bob recommended, and learnt all about polynominals.
NP> Remembering it al is another matter though :-)

Yes, I know the feeling. :-)

NP>  > NP> I just use a checksum of the ascii value of each byte
of the file.

NP>  > Not as effective as a CRC. A simple change like say 2 bytes being
NP>  > swapped will result in the same checksum for example. There was some
NP>  > commercial software I used once which must have used that or a similar
NP>  > approach for the user's registration details. rFakn was as valid a user
NP>  > as Frank. :-)

NP> I can see that now you have pointed it out.
NP> I have got a pice of software that must be done even worse, as upper or
NP> lower case on any letter is still acceptable.

That's not unreasonable, IMHO passwords should be case insensitive to
cater for those dickheads who leave their CapsLock on all the time. A
bit like programming languages, another reason why I try and avoid the
abortion that is 'C'. A programming language? I don't think so.

NP>  > I've just coded the 32-bit CRC which PKZIP & ARJ use in
(very) fast asm.
NP>  > It takes 6 minutes to calc the CRC of 5400 files, 220meg, on one of my
NP>  > hard disks. Also did the 16-bit CRC which all the other archivers use,
NP>  > and the 16-bit XModem one but didn't bother timing those.

NP> Is the 32 bit code available in an EXE file ??????

Not today, but tell me what you want and it'll be easy to make it so -
like, what do you want me to do with the generated CRC? Write it on the
screen? Append it to the .EXE file unless there's already one there in
which case report changes? I can do that, in fact I'd like to.

FYI I'm trying to build something which I've wanted for a long time, to
report *any* changes to files (fuck the archive flag, useless), to
maintain a complete catalogue of all my files (spread across several
computers physically separated (by miles)), mirror certain directories
between those physically separate machines, include the contents of
archives such as ZIP files in all of the above, etc, etc. It's a most
interesting exercise and means I have to develop *fast* disk I/O,
*fast* CRC routines, *fast* directory sorting, *fast* archive
extraction, etc - and then put it all together. :-)

And I'd quite like the opportunity to put some of what I've done to the
test by other users - but I need to know what you want.

Regards, fIM.

 * * Why does the AT&T logo look like the Death Star?
@EOT:

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