Re: [PATCH v2 17/21] rust: num: Add an upward alignment helper for usize

Alexandre Courbot
2025-05-01T21:02:59Z

On Fri May 2, 2025 at 12:19 AM JST, Timur Tabi wrote:
> On Thu, 2025-05-01 at 21:58 +0900, Alexandre Courbot wrote:
>
>
>> +impl UsizeAlign for usize {
>> +    fn align_up(mut self, align: usize) -> usize {
>> +        self = (self + align - 1) & !(align - 1);
>> +        self
>> +    }
>> +}
>> +
>> +/// Aligns `val` upwards to the nearest multiple of `align`.
>> +pub const fn usize_align_up(val: usize, align: usize) -> usize {
>> +    (val + align - 1) & !(align - 1)
>> +}
>
> Why not have usize_align_up() just return "val.align_up(align)"?
>
> But why why two versions at all? Is there any context where you could use one
> and not the other?

The second version can be used in const context to create values at
compile-time, something the first one cannot do. If we want to factorize
things out we can probably make the first version call the second one
though.