[PATCH v5 04/23] rust: add new `num` module with `PowerOfTwo` type

[John Hubbard]

On 6/12/25 1:05 PM, Boqun Feng wrote:
> On Thu, Jun 12, 2025 at 01:00:12PM -0700, John Hubbard wrote:
>> On 6/12/25 8:07 AM, Boqun Feng wrote:
>>> On Thu, Jun 12, 2025 at 11:01:32PM +0900, Alexandre Courbot wrote:
>> ...
>>>> +                #[inline(always)]
>>>> +                pub const fn align_down(self, value: $t) -> $t {
>>>
>>> I'm late to party, but could we instead implement:
>>>
>>>     pub const fn round_down<i32>(value: i32, shift: i32) -> i32 {
>>>         value & !((1 << shift) - 1)
>>>     }
>>>
>>>     pub const fn round_up<i32>(value: i32, shift: i32) -> i32 {
>>>         let mask = (1 << shift) - 1;
>>>         value.wrapping_add(mask) & !mask
>>>     }
>>
>> Just a naming concern here.
>>
>> The function name, and the "shift" argument is extremely odd there.
>> And that's because it is re-inventing the concept of align_down()
>> and align_up(), but with a misleading name and a hard to understand
>> "shift" argument.
>>
>> If you are "rounding" to a power of two, that's normally called
>> alignment, at least in kernel code. And if you are rounding to the
>> nearest...integer, for example, that's rounding.
>>
>> But "rounding" with a "shift" argument? That's a little too 
>> creative! :) 
>>
> 
> Oh, sorry, I should have mentioned where I got these names, see
> round_up() and round_down() in include/linux/math.h. But no objection to
> find a better name for "shift".

lol, perfect response! So my complaint is really about the kernel's existing
math.h, rather than your proposal. OK then. :)

thanks,
-- 
John Hubbard