Summary:
Using modulo on arbitrary integers to get random numbers [isn't correct](https://www.internalfb.com/diff/D31305392 (da13975a4f)?dst_version_fbid=311037904117090&transaction_fbid=550270779610744), as the distribution between numbers isn't fair (unless the size is a power of two).
This was raised on D31305392 (da13975a4f), but we decided to land that quickly to unblock builds before doing these changes.
I'm applying the changes suggested on D31305392 (da13975a4f). This is what this diff does:
- For all cases where we generate small numbers (up to 5), replace with call to `Gen::choose`, so `u32::arbitrary(g) % 3` becomes `g.choose(&[0, 1, 2]).unwrap()`.
- For generating numbers in range 0..=1, I instead replaced with generating a boolean, which gets rid of the `unreachable!` calls.
- I removed the code to generate numbers in range 0..=0.
- For generating larger numbers, I used `u64::arbitrary` instead, which should make things "less wrong".
Some things I assumed, but am happy to change before landing, just let me know:
- Theoretically we don't *need* to change the code for `% 2` and `% 4`, as the math checks out there. I changed it for consistency there, but am happy to change it back.
- Using boolean also wasn't suggested initially, I'm happy to change back.
Reviewed By: krallin
Differential Revision: D31379381
fbshipit-source-id: a0bac26ebabd32a6c65f717512de998ef5dc37c8
Mononoke is a next-generation server for the Mercurial source control
system, meant to scale up to accepting
thousands of commits every hour across millions of files. It is primarily
written in the Rust programming language.
Caveat Emptor
Mononoke is still in early stages of development. We are making it available now because we plan to
start making references to it from our other open source projects.
The version that we provide on GitHub does not build yet.
This is because the code is exported verbatim from an internal repository at Facebook, and
not all of the scaffolding from our internal repository can be easily extracted. The key areas
where we need to shore things up are:
Full support for a standard cargo build.
Open source replacements for Facebook-internal services (blob store, logging etc).
The current goal is to get Mononoke working on Linux. Other Unix-like OSes may
be supported in the future
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