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

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Message-ID: <aW9AibF0fWNYwRep@google.com>
Date: Tue, 20 Jan 2026 08:44:57 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Alexandre Courbot <acourbot@...dia.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 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) }

Alice