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]> --- 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),+) => { + $( + ::kernel::macros::paste! { + /// Last Set Bit: return the 1-based index of the last (i.e. most significant) set bit + /// in `v`. + /// + /// Equivalent to the C `fls` function. + /// + /// # Examples + /// + /// ``` + #[doc = concat!("use kernel::num::last_set_bit_", stringify!($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
