add new sfvxxhash format

[borco]

Please add a new file format sfvxxhash that uses xxhash instead of crc32.

Links:

• homepage: https://xxhash.com/
• python package: https://pypi.org/project/xxhash/

[lxp]

Thanks for your interest in cfv. I will not personally have time to implement various new formats like also with #9 and #41. However, I gladly accept pull requests implementing new useful formats.

[sarsolot]

Hi!

I have added support for xxHash (sfvxxh32, sfvxxh64, with sfvxxh -> XXH64). Functionally everything works as expected - checksums match both xxhsum and TurboSFV.

The only open question now is the output format for .xxh files. Currently, two formats are possible:

filename  hash        # current cfv style, same as .sfv
hash *filename        # xxhsum / TurboSFV style

cfv can easily verify both formats.

The question is about the default output when creating .xxh files.

Do you prefer:

• supporting both (verify both, create both but pick one default, second using switch - my preference), or
• choosing a single canonical format?

If both are acceptable (first option), which one should be the default? Happy to follow your preference or any existing convention for sfvxxh, if one exists (I could not find any formal standard).

[borco]

I don't see an issue to use switches to select the format (one for cfv/xxhsum and one for 32/64). You could use 64 as the default, if no specific 32 or 64 option is provided. The default extension could be .xxhash.

[sarsolot]

Thanks - just to clarify how I am planning to proceed for now:

• sfvxxh defaults to XXH64 (with sfvxxh32 / sfvxxh64 available).
• Use .xxh as the default extension - this is already used by TurboSFV and is common in practice, I haven’t seen .xxhash used as a convention anywhere.
• Default output format: hash *filename - this matches xxhsum / TurboSFV and works well with existing tools. cfv will verify both formats for compatibility.

Timing note: this branch is based on the existing BLAKE3 PR, so I’ll wait for that to land before opening the final sfvxxh PR.

[borco]

Sounds good. Thank you for working on this.