Add an equivalent to the `fls` (Find Last Set bit) C function to Rust
unsigned types.
It is to be first used by the nova-core driver.
Signed-off-by: Alexandre Courbot <acour...@nvidia.com>
---
rust/kernel/num.rs | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/rust/kernel/num.rs b/rust/kernel/num.rs
index
ee0f67ad1a89e69f5f8d2077eba5541b472e7d8a..934afe17719f789c569dbd54534adc2e26fe59f2
100644
--- a/rust/kernel/num.rs
+++ b/rust/kernel/num.rs
@@ -171,3 +171,34 @@ fn borrow(&self) -> &T {
&self.0
}
}
+
+macro_rules! impl_fls {
+ ($($t:ty),+) => {
+ $(
+ ::kernel::macros::paste! {
+ /// Find Last Set Bit: return the 1-based index of the last (i.e.
most significant) set
+ /// bit in `v`.
+ ///
+ /// Equivalent to the C `fls` function.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use kernel::num::fls_u32;
+ ///
+ /// assert_eq!(fls_u32(0x0), 0);
+ /// assert_eq!(fls_u32(0x1), 1);
+ /// assert_eq!(fls_u32(0x10), 5);
+ /// assert_eq!(fls_u32(0xffff), 16);
+ /// assert_eq!(fls_u32(0x8000_0000), 32);
+ /// ```
+ #[inline(always)]
+ pub const fn [<fls_ $t>](v: $t) -> u32 {
+ $t::BITS - v.leading_zeros()
+ }
+ }
+ )+
+ };
+}
+
+impl_fls!(usize, u8, u16, u32, u64, u128);
--
2.49.0
