linux-kernel - Re: [PATCH 1/6] rust: num: add `shr` and `shl` methods to `Bounded`

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <DFTFJV461GAP.1AUIWIYQGFWSV@nvidia.com>
Date: Tue, 20 Jan 2026 21:53:58 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Miguel Ojeda" <ojeda@...nel.org>, "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>, "Yury Norov" <yury.norov@...il.com>,
 "John Hubbard" <jhubbard@...dia.com>, "Alistair Popple"
 <apopple@...dia.com>, "Joel Fernandes" <joelagnelf@...dia.com>, "Timur
 Tabi" <ttabi@...dia.com>, "Edwin Peer" <epeer@...dia.com>, "Eliot Courtney"
 <ecourtney@...dia.com>, "Daniel Almeida" <daniel.almeida@...labora.com>,
 "Dirk Behme" <dirk.behme@...bosch.com>, "Steven Price"
 <steven.price@....com>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] rust: num: add `shr` and `shl` methods to `Bounded`

On Tue Jan 20, 2026 at 5:44 PM JST, Alice Ryhl wrote:
> On Tue, Jan 20, 2026 at 03:17:54PM +0900, Alexandre Courbot wrote:
>> Shifting a `Bounded` left or right changes the number of bits required
>> to represent the value. Add methods that perform the shift and return a
>> `Bounded` with the appropriately adjusted bit width.
>> 
>> These methods are particularly useful for bitfield extraction.
>> 
>> Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
>> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
>
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
>
>> +    /// Right-shifts `self` by `SHIFT` and returns the result as a `Bounded<_, { N - SHIFT }>`.
>> +    ///
>> +    /// # Examples
>> +    ///
>> +    /// ```
>> +    /// use kernel::num::Bounded;
>> +    ///
>> +    /// let v = Bounded::<u32, 16>::new::<0xff00>();
>> +    /// let v_shifted: Bounded::<u32, 8> = v.shr::<8, _>();
>> +    ///
>> +    /// assert_eq!(v_shifted.get(), 0xff);
>> +    /// ```
>> +    pub fn shr<const SHIFT: u32, const RES: u32>(self) -> Bounded<T, RES> {
>> +        const { assert!(RES == N - SHIFT) }
>
> In principle this could be
>
> const { assert!(RES >= N - SHIFT) }

Oh, that's right and that's also more flexible - thanks, will do that for v2.