CRC-32 and CRC-64 operating parameters for WIN7 x32 and x64?

[Jonathan Broyles]

Hi, after installing 7zip on my Win7 x64 computer, I noticed that I now have CRC-32 and CRC-64 available to check files with. I would like to use these at work but I need to verify them against known CRC programs and files. Does any one know what the following parameters are that are used in each of these programs? Thanks, Jonathan

• Polynominal
• Initial CRC value
• Type of algorithm, Direct no augmented zero bits or augmented zero bits
• Value xor'd with final CRC value
• Are data bytes reflected before processing (UART) or not
• Is CRC reflected before final Xor
• Is the data/msg stream reversed or not before processing

[Igor Pavlov]

CRC-32 - same as ZIP, Gzip, xz.
CRC-64 - same as xz utils (wikipedia writes that it's ECMA-182).

So you can check any details in source code of zip/gzip/7z/xz.
And you can check exact digest values with sofware 7-Zip / xz utils / gzip / info-zip.

[AmigoJack]

The CRC-64 parameters 7-Zip is using isn't ECMA - as per https://reveng.sourceforge.io/crc-catalogue/17plus.htm#crc.cat.crc-64-xz that misidentification often happens and it's actually the XZ variant. The CRC-32 parameters 7-Zip is using are the same as used by PKZIP and XZ - as per https://reveng.sourceforge.io/crc-catalogue/17plus.htm#crc.cat.crc-32-iso-hdlc the variant is also named ISO-HDLC.

I've been struggling with that too, as the correct CRC-64/ECMA-182 produces different results. https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Polynomial_representations_of_cyclic_redundancy_checks only distinguishes by polynomials as parameter, not others. And nobody corrects it, although the reference of https://en.wikipedia.org/wiki/XZ_Utils does not mention anything about CRC at all. But https://tukaani.org/xz/xz-file-format.txt clearly shows in its code that the initialization is 0xFFFFffffFFFFffff, so it can't be ECMA.