Shifting a `Bounded` left or right changes the number of bits required
to represent the value. Add methods that perform the shift and return a
`Bounded` with the appropriately adjusted bit width.
These methods are particularly useful for bitfield extraction.
Suggested-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
rust/kernel/num/bounded.rs | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)
diff --git a/rust/kernel/num/bounded.rs b/rust/kernel/num/bounded.rs
index f870080af8ac..4b929762d5c2 100644
--- a/rust/kernel/num/bounded.rs
+++ b/rust/kernel/num/bounded.rs
@@ -470,6 +470,48 @@ pub fn cast<U>(self) -> Bounded<U, N>
// `N` bits, and with the same signedness.
Bounded::__new(value)
}
+
+ /// Right-shifts `self` by `SHIFT` and returns the result as a `Bounded<_, RES>`, where `RES >=
+ /// N - SHIFT`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::num::Bounded;
+ ///
+ /// let v = Bounded::<u32, 16>::new::<0xff00>();
+ /// let v_shifted: Bounded::<u32, 8> = v.shr::<8, _>();
+ ///
+ /// assert_eq!(v_shifted.get(), 0xff);
+ /// ```
+ pub fn shr<const SHIFT: u32, const RES: u32>(self) -> Bounded<T, RES> {
+ const { assert!(RES >= N - SHIFT) }
+
+ // SAFETY: We shift the value right by `SHIFT`, reducing the number of bits needed to
+ // represent the shifted value by as much, and just asserted that `RES == N - SHIFT`.
+ unsafe { Bounded::__new(self.0 >> SHIFT) }
+ }
+
+ /// Left-shifts `self` by `SHIFT` and returns the result as a `Bounded<_, RES>`, where `RES >=
+ /// N + SHIFT`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::num::Bounded;
+ ///
+ /// let v = Bounded::<u32, 8>::new::<0xff>();
+ /// let v_shifted: Bounded::<u32, 16> = v.shl::<8, _>();
+ ///
+ /// assert_eq!(v_shifted.get(), 0xff00);
+ /// ```
+ pub fn shl<const SHIFT: u32, const RES: u32>(self) -> Bounded<T, RES> {
+ const { assert!(RES >= N + SHIFT) }
+
+ // SAFETY: We shift the value left by `SHIFT`, augmenting the number of bits needed to
+ // represent the shifted value by as much, and just asserted that `RES == N + SHIFT`.
+ unsafe { Bounded::__new(self.0 << SHIFT) }
+ }
}
impl<T, const N: u32> Deref for Bounded<T, N>
--
2.52.0