On Fri, Jun 20, 2025 at 10:14:52PM +0900, Alexandre Courbot wrote: > 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 <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]> > rust/kernel/num.rs | 38 ++++++++++++++++++++++++++++++++++++++ > 1 file changed, 38 insertions(+) > > diff --git a/rust/kernel/num.rs b/rust/kernel/num.rs > index > 6ecff037893dd25420a6369ea0cd6adbe3460b29..95766201a7cf208989f37ecbc6d54d264385a754 > 100644 > --- a/rust/kernel/num.rs > +++ b/rust/kernel/num.rs > @@ -161,3 +161,41 @@ pub const fn align_up(self, value: $t) -> $t { > } > > power_of_two_impl!(usize, u8, u16, u32, u64, u128); > + > +macro_rules! impl_last_set_bit { > + ($($t:ty),+) => { > + $( > + ::kernel::macros::paste! { I think this would read slightly nicer with the paste! invocation on the outer scope. $(::kernel::macros::paste! { ... })+ > + /// Last Set Bit: return the 1-based index of the last (i.e. > most significant) set bit > + /// in `v`. > + /// > + /// Equivalent to the C `fls` function. > + /// > + /// # Examples > + /// > + /// ``` > + #[doc = concat!("use kernel::num::last_set_bit_", > stringify!($t), ";")] > + /// > + #[doc = concat!("assert_eq!(last_set_bit_", stringify!($t), > "(0x0), 0);")] > + #[doc = concat!("assert_eq!(last_set_bit_", stringify!($t), > "(0x1), 1);")] > + #[doc = concat!("assert_eq!(last_set_bit_", stringify!($t), > "(0x10), 5);")] > + #[doc = concat!("assert_eq!(last_set_bit_", stringify!($t), > "(0x1f), 5);")] > + #[doc = concat!( > + "assert_eq!(last_set_bit_", > + stringify!($t), > + "(", > + stringify!($t), > + "::MAX), ", > + stringify!($t), "::BITS);" > + )] > + /// ``` > + #[inline(always)] > + pub const fn [<last_set_bit_ $t>](v: $t) -> u32 { > + $t::BITS - v.leading_zeros() > + } > + } > + )+ > + }; > +} > + > +impl_last_set_bit!(usize, u8, u16, u32, u64, u128); > > -- > 2.49.0 >
