Checksums are not portable

[aleksa2808]

Checksums are not portable

[johanhelsing]

Merging #94 first would make fixing this a bit simpler, because then it's just one place to change the hasher.

[johanhelsing]

@aleksa2808 Thanks for the detailed write-up. Do you want to contribute this as a PR (casting to u64 and replacing with SeaHash or another portable hasher)?

[aleksa2808]

Sure, I can make this a PR. I'm just not sure what to do with SeaHash as I'm currently using my own fork of it where I intentionally panic when trying to hash usize/isize values since this would lead to desyncs on different architectures. I could use the original, non-panicky version, but I feel like users could easily make the mistake of hashing some .len() value for example and in this case I think it is good to error out (or better yet prevent compilation if possible). Do you have any ideas regarding this?

[johanhelsing]

We don't necessarily have to do everything in one go. We could do it like this:

1. Get rid of usize in internal checksums
2. Change aHash to SeaHash or something else
3. Document this gotcha (#35)

[aleksa2808]

Hey @johanhelsing, sorry for the late reply. I created a PR for this now with both changes included as they are both essential to calculate checksums in a portable manner.

Additionally, regarding the mentioned SeaHash fork, in this PR I used the regular, crates.io provided version. This means that users will still be able to use usize/isize types in their code which would break portability, so it is a good idea to have this mentioned in a gotcha.