linux.git/rust/kernel/num.rs, branch v7.3-rc2 Linux kernel source tree rust: add functions and traits for lossless integer conversions 2026-08-13T11:41:28+00:00 Alexandre Courbot acourbot@nvidia.com 2026-08-06T07:35:53+00:00 47f27155f17498fccb1f222f79089642337498a9 The core library's `From` implementations do not cover conversions that are not portable or future-proof. For instance, even though it is safe today, `From<usize>` is not implemented for `u64` because of the possibility of supporting larger-than-64bit architectures in the future. However, the kernel supports a narrower set of architectures, with a considerable amount of code that is architecture-specific. This makes it helpful and desirable to provide more infallible conversions, lest we rely on the `as` keyword and carry the risk of silently losing data. Thus, introduce a new module `num::casts` that provides safe const functions performing more conversions allowed by the build target, as well as `FromSafeCast` and `IntoSafeCast` traits that are just extensions of `From` and `Into` to conversions that are known to be lossless. Some conversions are architecture-specific: for instance, converting a `u64` to a `usize` is only lossless on 64-bit platforms. These conversions are made available via a dedicated `arch` sub-module. Suggested-by: Danilo Krummrich <dakr@kernel.org> Link: https://lore.kernel.org/rust-for-linux/DDK4KADWJHMG.1FUPL3SDR26XF@kernel.org/ Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> Reviewed-by: Danilo Krummrich <dakr@kernel.org> Link: https://patch.msgid.link/20260806-as_casts-v2-1-cb76a4d3a6ef@nvidia.com [ Added a few more intra-doc links. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org> 
The core library's `From` implementations do not cover conversions that
are not portable or future-proof. For instance, even though it is safe
today, `From<usize>` is not implemented for `u64` because of the
possibility of supporting larger-than-64bit architectures in the future.

However, the kernel supports a narrower set of architectures, with a
considerable amount of code that is architecture-specific. This makes it
helpful and desirable to provide more infallible conversions, lest we
rely on the `as` keyword and carry the risk of silently losing data.

Thus, introduce a new module `num::casts` that provides safe const
functions performing more conversions allowed by the build target, as
well as `FromSafeCast` and `IntoSafeCast` traits that are just
extensions of `From` and `Into` to conversions that are known to be
lossless.

Some conversions are architecture-specific: for instance, converting a
`u64` to a `usize` is only lossless on 64-bit platforms. These
conversions are made available via a dedicated `arch` sub-module.

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/rust-for-linux/DDK4KADWJHMG.1FUPL3SDR26XF@kernel.org/
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20260806-as_casts-v2-1-cb76a4d3a6ef@nvidia.com
[ Added a few more intra-doc links. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
rust: num: add Bounded integer wrapping type 2025-11-18T23:22:24+00:00 Alexandre Courbot acourbot@nvidia.com 2025-11-08T02:23:48+00:00 01e345e82ec3a5a7edeb9fa0dcb7fd4b0e5c534e Add the `Bounded` integer wrapper type, which restricts the number of bits allowed to represent of value. This is useful to e.g. enforce guarantees when working with bitfields that have an arbitrary number of bits. Alongside this type, provide many `From` and `TryFrom` implementations are to reduce friction when using with regular integer types. Proxy implementations of common integer operations are also provided. Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Link: https://patch.msgid.link/20251108-bounded_ints-v4-2-c9342ac7ebd1@nvidia.com [ Added intra-doc link. Fixed a few other nits. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org> 
Add the `Bounded` integer wrapper type, which restricts the number of
bits allowed to represent of value.

This is useful to e.g. enforce guarantees when working with bitfields
that have an arbitrary number of bits.

Alongside this type, provide many `From` and `TryFrom` implementations
are to reduce friction when using with regular integer types. Proxy
implementations of common integer operations are also provided.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251108-bounded_ints-v4-2-c9342ac7ebd1@nvidia.com
[ Added intra-doc link. Fixed a few other nits. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
rust: add num module and Integer trait 2025-11-17T21:56:23+00:00 Alexandre Courbot acourbot@nvidia.com 2025-11-08T02:23:47+00:00 90f3df4fdfb682e2394ee3f97dfe91a402d5c46a Introduce the `num` module, which will provide numerical extensions and utilities for the kernel. For now, introduce the `Integer` trait, which is implemented for all primitive integer types to provides their core properties to generic code. Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Link: https://patch.msgid.link/20251108-bounded_ints-v4-1-c9342ac7ebd1@nvidia.com Signed-off-by: Miguel Ojeda <ojeda@kernel.org> 
Introduce the `num` module, which will provide numerical extensions and
utilities for the kernel.

For now, introduce the `Integer` trait, which is implemented for all
primitive integer types to provides their core properties to generic
code.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251108-bounded_ints-v4-1-c9342ac7ebd1@nvidia.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>