linux-kernel - Re: [PATCH 1/3] rust: add `num` module with `PowerOfTwo` type

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Message-Id: <DBRZX7EAK13R.LTIJJPA9CCSO@nvidia.com>
Date: Sat, 02 Aug 2025 23:02:32 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Miguel Ojeda" <miguel.ojeda.sandonis@...il.com>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng"
 <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Trevor
 Gross" <tmgross@...ch.edu>, "Danilo Krummrich" <dakr@...nel.org>,
 <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
 <nouveau@...ts.freedesktop.org>, "Nouveau"
 <nouveau-bounces@...ts.freedesktop.org>
Subject: Re: [PATCH 1/3] rust: add `num` module with `PowerOfTwo` type

On Fri Jun 20, 2025 at 11:02 PM JST, Alice Ryhl wrote:
> On Fri, Jun 20, 2025 at 3:59 PM Alexandre Courbot <acourbot@...dia.com> wrote:
>> > Similarly, if they stabilize the `Alignment` one (only) and we end up
>> > only using our `PowerOfTwo<T>` for `usize` and those use cases, then
>> > we should consider using the upstream one (and adding any/all methods
>> > that we need).
>>
>> `Alignment` is very close to what we need, so I don't see a reason to
>> not adopt the same name at the very least.
>>
>> This reminds me that I should also check whether upstream Rust would be
>> interested in `prev_multiple_of` and `last_set_bit`. The docs I've read
>> for contributing looked a bit intimidating, with RFCs to write and all.
>> Would you have a pointer for where I should start? Maybe a Zulip thread?
>
> If you want to add a new library function, the correct procedure would
> be opening an ACP, which is more light-weight than the RFC process:
> https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html
>
> RFCs are mainly for much bigger changes.

Belated thanks for the suggestion; I have finally opened an ACP for
`last_set_bit` (and `first_set_bit` while we are at it):
https://github.com/rust-lang/libs-team/issues/631

I am still entangled with how to best leverage `Alignment` for our
purposes, but think I am getting close to a v2 of this patchset.