linux-kernel - Re: [PATCH v2 17/21] rust: num: Add an upward alignment helper for usize

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Message-Id: <D9L4MCKPAUE9.57CNHP46R2IC@nvidia.com>
Date: Fri, 02 May 2025 06:02:50 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Timur Tabi" <ttabi@...dia.com>, "dakr@...nel.org" <dakr@...nel.org>,
 "a.hindborg@...nel.org" <a.hindborg@...nel.org>, "ojeda@...nel.org"
 <ojeda@...nel.org>, "boqun.feng@...il.com" <boqun.feng@...il.com>,
 "simona@...ll.ch" <simona@...ll.ch>, "tmgross@...ch.edu"
 <tmgross@...ch.edu>, "alex.gaynor@...il.com" <alex.gaynor@...il.com>,
 "tzimmermann@...e.de" <tzimmermann@...e.de>, "corbet@....net"
 <corbet@....net>, "mripard@...nel.org" <mripard@...nel.org>,
 "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
 "benno.lossin@...ton.me" <benno.lossin@...ton.me>,
 "bjorn3_gh@...tonmail.com" <bjorn3_gh@...tonmail.com>, "airlied@...il.com"
 <airlied@...il.com>, "aliceryhl@...gle.com" <aliceryhl@...gle.com>,
 "gary@...yguo.net" <gary@...yguo.net>
Cc: "Alistair Popple" <apopple@...dia.com>, "John Hubbard"
 <jhubbard@...dia.com>, "rust-for-linux@...r.kernel.org"
 <rust-for-linux@...r.kernel.org>, "dri-devel@...ts.freedesktop.org"
 <dri-devel@...ts.freedesktop.org>, "nouveau@...ts.freedesktop.org"
 <nouveau@...ts.freedesktop.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "Joel Fernandes" <joelagnelf@...dia.com>,
 "Ben Skeggs" <bskeggs@...dia.com>
Subject: Re: [PATCH v2 17/21] rust: num: Add an upward alignment helper for
 usize

On Fri May 2, 2025 at 12:19 AM JST, Timur Tabi wrote:
> On Thu, 2025-05-01 at 21:58 +0900, Alexandre Courbot wrote:
>
>
>> +impl UsizeAlign for usize {
>> +    fn align_up(mut self, align: usize) -> usize {
>> +        self = (self + align - 1) & !(align - 1);
>> +        self
>> +    }
>> +}
>> +
>> +/// Aligns `val` upwards to the nearest multiple of `align`.
>> +pub const fn usize_align_up(val: usize, align: usize) -> usize {
>> +    (val + align - 1) & !(align - 1)
>> +}
>
> Why not have usize_align_up() just return "val.align_up(align)"?
>
> But why why two versions at all?  Is there any context where you could use one
> and not the other?

The second version can be used in const context to create values at
compile-time, something the first one cannot do. If we want to factorize
things out we can probably make the first version call the second one
though.