Hi Alex,
> On 17 Feb 2025, at 11:04, Alexandre Courbot <acour...@nvidia.com> wrote:
>
> It is common to build a u64 from its high and low parts obtained from
> two 32-bit registers. Conversely, it is also common to split a u64 into
> two u32s to write them into registers. Add an extension trait for u64
> that implement these methods in a new `num` module.
Thank you for working on that. I find myself doing this manually extremely
often indeed.
>
> It is expected that this trait will be extended with other useful
> operations, and similar extension traits implemented for other types.
>
> Signed-off-by: Alexandre Courbot <acour...@nvidia.com>
> ---
> rust/kernel/lib.rs | 1 +
> rust/kernel/num.rs | 32 ++++++++++++++++++++++++++++++++
> 2 files changed, 33 insertions(+)
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index
> 496ed32b0911a9fdbce5d26738b9cf7ef910b269..8c0c7c20a16aa96e3d3e444be3e03878650ddf77
> 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -59,6 +59,7 @@
> pub mod miscdevice;
> #[cfg(CONFIG_NET)]
> pub mod net;
> +pub mod num;
> pub mod of;
> pub mod page;
> #[cfg(CONFIG_PCI)]
> diff --git a/rust/kernel/num.rs b/rust/kernel/num.rs
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..5e714cbda4575b8d74f50660580dc4c5683f8c2b
> --- /dev/null
> +++ b/rust/kernel/num.rs
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Numerical and binary utilities for primitive types.
> +
> +/// Useful operations for `u64`.
> +pub trait U64Ext {
> + /// Build a `u64` by combining its `high` and `low` parts.
> + ///
> + /// ```
> + /// use kernel::num::U64Ext;
> + /// assert_eq!(u64::from_u32s(0x01234567, 0x89abcdef),
> 0x01234567_89abcdef);
> + /// ```
> + fn from_u32s(high: u32, low: u32) -> Self;
> +
> + /// Returns the `(high, low)` u32s that constitute `self`.
> + ///
> + /// ```
> + /// use kernel::num::U64Ext;
> + /// assert_eq!(u64::into_u32s(0x01234567_89abcdef), (0x1234567,
> 0x89abcdef));
> + /// ```
> + fn into_u32s(self) -> (u32, u32);
> +}
> +
> +impl U64Ext for u64 {
> + fn from_u32s(high: u32, low: u32) -> Self {
> + ((high as u64) << u32::BITS) | low as u64
> + }
> +
> + fn into_u32s(self) -> (u32, u32) {
I wonder if a struct would make more sense here.
Just recently I had to debug an issue where I forgot the
right order for code I had just written. Something like:
let (pgcount, pgsize) = foo(); where the function actually
returned (pgsize, pgcount).
A proper struct with `high` and `low` might be more verbose, but
it rules out this issue.
> + ((self >> u32::BITS) as u32, self as u32)
> + }
> +}
>
> --
> 2.48.1
>
— Daniel
>
