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

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Message-Id: <DBSTIFXLOTMQ.3TTS2O1PDIR95@nvidia.com>
Date: Sun, 03 Aug 2025 22:13:49 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Miguel Ojeda" <miguel.ojeda.sandonis@...il.com>
Cc: "Alice Ryhl" <aliceryhl@...gle.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 Sat Aug 2, 2025 at 11:18 PM JST, Miguel Ojeda wrote:
> On Sat, Aug 2, 2025 at 4:02 PM Alexandre Courbot <acourbot@...dia.com> wrote:
>>
>> 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.
>
> Thanks for filling that one -- linked now from our usual lists :)
>
>     https://github.com/Rust-for-Linux/linux/issues/514

We got some interesting feedback on the ACP already. I have been pointed
to `checked_ilog2` as an equivalent of `last_set_bit`, and it *does*
indeed work well as a replacement - with the caveat that the name is
not very natural to me (or anyone familiar with the C interface). Is
this something we can live with? If we decide to go with the existing
standard library method, how can we make sure that folks looking for an
equivalent of `fls` find `checked_ilog2`?