Re: [PATCH 1/2] rust: add BitInt integer wrapping type

Alexandre Courbot
2025-11-03T14:44:31Z

On Mon Nov 3, 2025 at 11:26 PM JST, Yury Norov wrote:
> On Mon, Nov 03, 2025 at 03:10:01PM +0100, Miguel Ojeda wrote:
>> On Mon, Nov 3, 2025 at 3:17 AM Yury Norov <yury.norov@gmail.com> wrote:
>> >
>> > Rust _must_ do the same thing to at least be arithmetically
>> > compatible to the big brother.
>>
>> No, Rust doesn't need to do anything of the sort, sorry.
>>
>> The point here is not to copy what C does, but to improve on it.
>>
>> In particular, we definitely do not want to have anything like integer
>> promotions and arithmetic conversions from C.
>
> This is exactly what the patch does:
>
> +/// let v = BitInt::<u8, 4>::from_expr(15);
> +///
> +/// // Common operations are supported against the backing type.
> +/// assert_eq!(v + 5, 20);
> +/// assert_eq!(v / 3, 5);

That's incorrect. `v` is backed by a u8, thus the RHS `5` is also a u8
(and so is the result, `20`).