[PATCH 01/16] rust: add useful ops for u64

Alexandre Courbot
2025-04-20T12:20:00Z

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.

It is expected that this trait will be extended with other useful
operations, and similar extension traits implemented for other types.

Reviewed-by: Sergio González Collado <sergio.collado@gmail.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
rust/kernel/lib.rs | 1 +
rust/kernel/num.rs | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 53 insertions(+)

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 55a8dfeece0b27f188456a9eaebd1045c4cafbcb..e30d2c075a3607f6ea40c901b3281e8798e81260 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -65,6 +65,7 @@
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..9b93db6528eef131fb74c1289f1e152cc2a13168
--- /dev/null
+++ b/rust/kernel/num.rs
@@ -0,0 +1,52 @@
+// 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 upper 32 bits of `self`.
+ fn upper_32_bits(self) -> u32;
+
+ /// Returns the lower 32 bits of `self`.
+ fn lower_32_bits(self) -> u32;
+}
+
+impl U64Ext for u64 {
+ fn from_u32s(high: u32, low: u32) -> Self {
+ ((high as u64) << u32::BITS) | low as u64
+ }
+
+ fn upper_32_bits(self) -> u32 {
+ (self >> u32::BITS) as u32
+ }
+
+ fn lower_32_bits(self) -> u32 {
+ self as u32
+ }
+}
+
+/// Same as [`U64Ext::upper_32_bits`], but defined outside of the trait so it can be used in a
+/// `const` context.
+pub const fn upper_32_bits(v: u64) -> u32 {
+ (v >> u32::BITS) as u32
+}
+
+/// Same as [`U64Ext::lower_32_bits`], but defined outside of the trait so it can be used in a
+/// `const` context.
+pub const fn lower_32_bits(v: u64) -> u32 {
+ v as u32
+}
+
+/// Same as [`U64Ext::from_u32s`], but defined outside of the trait so it can be used in a `const`
+/// context.
+pub const fn u64_from_u32s(high: u32, low: u32) -> u64 {
+ ((high as u64) << u32::BITS) | low as u64
+}

--
2.49.0