[PATCH 1/3] rust: add `num` module with `PowerOfTwo` type

[Benno Lossin]

On Fri Jul 25, 2025 at 5:38 AM CEST, Alexandre Courbot wrote:
> Hi Benno,
>
> Sorry, took some time to come back to this!

No worries!

> On Sun Jun 22, 2025 at 5:11 PM JST, Benno Lossin wrote:
>> On Fri Jun 20, 2025 at 3:14 PM CEST, Alexandre Courbot wrote:
>>> +                /// Returns the value of this instance.
>>> +                ///
>>> +                /// It is guaranteed to be a power of two.
>>> +                ///
>>> +                /// # Examples
>>> +                ///
>>> +                /// ```
>>> +                /// use kernel::num::PowerOfTwo;
>>> +                ///
>>> +                #[doc = concat!("let v = PowerOfTwo::<", stringify!($t), ">::new(16);")]
>>> +                /// assert_eq!(v.value(), 16);
>>> +                /// ```
>>> +                #[inline(always)]
>>> +                pub const fn value(self) -> $t {
>>> +                    self.0
>>
>> Let's add:
>>
>>     if !self.0.is_power_of_two() {
>>         core::hint::unreachable_unchecked()
>>     }
>>     self.0
>
> Sure. Is it to enable compiler optimizations by making assumptions about
> the returned value?

Exactly, it will for example turn dividing by it into a right shift and
prevent a branch for the zero check.

---
Cheers,
Benno