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

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Message-ID: <7481f03b-3fb0-499e-b200-b3366334adc2@nvidia.com>
Date: Thu, 1 May 2025 11:22:22 -0400
From: Joel Fernandes <joelagnelf@...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>,
 Alexandre Courbot <acourbot@...dia.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>,
 Ben Skeggs <bskeggs@...dia.com>
Subject: Re: [PATCH v2 17/21] rust: num: Add an upward alignment helper for
 usize



On 5/1/2025 11:19 AM, 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?
> 
I can't remember now but when I tried that, I got compiler errors (because val
is immutable?).

Also not mutating it like that matches the pattern in the rest of this file so
I'd leave it as-is.

Thanks.