Hi Alex,
> On 4 Aug 2025, at 08:45, Alexandre Courbot <acourbot at nvidia.com>
wrote:
>
> Rust provides traits for standard arithmetic and logic operations, but
> in the context of the kernel we often need to consider overflows. The
> checked Rust arithmetic methods are unfortunately not behind a trait,
> which makes them unavailable to generic code.
>
> As a start, add the `CheckedAdd` trait providing the `checked_add`
> operation and implement it for all integer types. Its name and location
> are inspired by the user-space `num` crate.
>
> This trait is to be first used by the `Alignment` type.
>
> Signed-off-by: Alexandre Courbot <acourbot at nvidia.com>
> ---
> rust/kernel/lib.rs | 1 +
> rust/kernel/num.rs | 28 ++++++++++++++++++++++++++++
> 2 files changed, 29 insertions(+)
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index
6b4774b2b1c37f4da1866e993be6230bc6715841..2955f65da1278dd4cba1e4272ff178b8211a892c
100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -89,6 +89,7 @@
> pub mod mm;
> #[cfg(CONFIG_NET)]
> pub mod net;
> +pub mod num;
> pub mod of;
> #[cfg(CONFIG_PM_OPP)]
> pub mod opp;
> diff --git a/rust/kernel/num.rs b/rust/kernel/num.rs
> new file mode 100644
> index
0000000000000000000000000000000000000000..c81bb046078b70c321dd52aa9c2b5518be49d249
> --- /dev/null
> +++ b/rust/kernel/num.rs
> @@ -0,0 +1,28 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Numerical and binary utilities for primitive types.
> +
> +use core::ops::Add;
> +
> +/// Trait for performing a checked addition that returns `None` if the
operation would overflow.
nit: this can be [`None`] instead, which will let users click on it in the docs.
This is of course pretty frivolous.
> +///
> +/// This trait exists in order to represent scalar types already having a
`checked_add` method in
> +/// generic code.
Maybe ?scalar types that already have a `checked_add` method?
But overall I feel like the whole sentence is a bit hard to parse, JFYI.
> +pub trait CheckedAdd: Sized + Add<Self, Output = Self> {
> + /// Computes `self + rhs`, returning `None` if an overflow would
occur.
> + fn checked_add(self, rhs: Self) -> Option<Self>;
> +}
> +
> +macro_rules! impl_checked_add {
> + ($($t:ty),*) => {
> + $(
> + impl CheckedAdd for $t {
> + fn checked_add(self, rhs: Self) -> Option<Self> {
> + self.checked_add(rhs)
> + }
> + }
> + )*
> + };
> +}
> +
> +impl_checked_add!(u8, u16, u32, u64, usize, i8, i16, i32, i64, isize);
>
> --
> 2.50.1
>
>
Reviewed-by: Daniel Almeida <daniel.almeida at collabora.com>