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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>
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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>
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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>
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Alexandre Courbot