linux-kernel - Re: [PATCH 1/2] rust: add BitInt integer wrapping type

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Message-Id: <DDZ41ZUCG09M.KYZOZGQ2TRGT@nvidia.com>
Date: Mon, 03 Nov 2025 22:57:28 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Alexandre Courbot" <acourbot@...dia.com>, "Yury Norov"
 <yury.norov@...il.com>
Cc: "Alice Ryhl" <aliceryhl@...gle.com>, "Danilo Krummrich"
 <dakr@...nel.org>, "Miguel Ojeda" <ojeda@...nel.org>, "Joel Fernandes"
 <joelagnelf@...dia.com>, "Jesung Yang" <y.j3ms.n@...il.com>, "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>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH 1/2] rust: add BitInt integer wrapping type

On Mon Nov 3, 2025 at 10:42 PM JST, Alexandre Courbot wrote:
<snip>
> After comparing this implementation with C's `_BitInt`, I have also come
> to a more fundamental divergence between the two.
>
> The C `_BitInt` is used to express numbers with an arbitrary number of
> bits - which could be less than a primitive type, but also *more* - for
> instance a `_BitInt(4094)` is a valid thing!
>
> Which is really cool, but also not something we need or want in the
> kernel. Our purposes here is strictly to limit the width of existing
> primitive types to provide extra guarantees about the code. And even if
> we wanted to mimic the C `_BitInt`, we simply couldn't without compiler
> support as literal values larger than a primitive type cannot even be
> expressed.
>
> So although I liked the `BitInt` name, that makes it quite a bit
> misleading for our type as users could think that they will have an
> equivalent to the C namesake, while the purpose and use is different.
>
> The original `BoundedInt` name was a more accurate fit IMHO, but I hope
> we can find something shorter.

Actually - the core library names similar wrapping types `NonZero` or
`Wrapping` - not `NonZeroInt` or `WrappingInt`. So this type could just
be called `Bounded`, as its generic parameter makes it clear what it
sets the bounds of anyway.