linux-kernel - Re: [PATCH v5 05/23] rust: num: add the `fls` operation

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Message-Id: <DAN1XS7Z0AFO.3S7PRNH5FWWV4@nvidia.com>
Date: Sun, 15 Jun 2025 19:58:01 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Alexandre Courbot" <acourbot@...dia.com>, "Miguel Ojeda"
 <miguel.ojeda.sandonis@...il.com>
Cc: "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>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "Danilo Krummrich" <dakr@...nel.org>, "David Airlie" <airlied@...il.com>,
 "Simona Vetter" <simona@...ll.ch>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "Benno Lossin"
 <lossin@...nel.org>, "John Hubbard" <jhubbard@...dia.com>, "Ben Skeggs"
 <bskeggs@...dia.com>, "Joel Fernandes" <joelagnelf@...dia.com>, "Timur
 Tabi" <ttabi@...dia.com>, "Alistair Popple" <apopple@...dia.com>,
 <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
 <nouveau@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v5 05/23] rust: num: add the `fls` operation

On Sun Jun 15, 2025 at 7:51 PM JST, Alexandre Courbot wrote:
> On Sun Jun 15, 2025 at 6:37 PM JST, Miguel Ojeda wrote:
>> On Thu, Jun 12, 2025 at 4:02 PM Alexandre Courbot <acourbot@...dia.com> wrote:
>>>
>>> +            /// ```
>>> +            /// use kernel::num::fls_u32;
>>> +            ///
>>> +            /// assert_eq!(fls_u32(0x0), 0);
>>> +            /// assert_eq!(fls_u32(0x1), 1);
>>> +            /// assert_eq!(fls_u32(0x10), 5);
>>> +            /// assert_eq!(fls_u32(0xffff), 16);
>>> +            /// assert_eq!(fls_u32(0x8000_0000), 32);
>>> +            /// ```
>>
>> For a future patch series: this could provide examples per type
>> (passing them in the `impl_fls!` call).
>>
>> I can create a good first issue if this lands and it is not somewhere already.
>
> I was worried that the examples would be mostly duplicated, although
> it is true that seeing how the function behaves at the limits of each
> type is valuable. I'll prepare a patch to either squash for v6 or submit
> as a follow-up.

Also, although this will work nicely for `impl_fls!` which is a single
function, I'm afraid this won't scale well for `power_of_two_impl!`,
which defines 6 functions per type... Any suggestions for this case?