Re: [PATCH v2 2/3] rust: alloc: add Vec::resize method

[Tamir Duberstein]

On Wed, Mar 19, 2025 at 12:06 PM Miguel Ojeda
<miguel.ojeda.sandonis@xxxxxxxxx> wrote:
>
> On Wed, Mar 19, 2025 at 4:59 PM Tamir Duberstein <tamird@xxxxxxxxx> wrote:
> >
> > If we're talking about the same thing then I think we're both wrong
> > and the correct phrasing would have been: "you can avoid underflow
> > checking when CONFIG_RUST_OVERFLOW_CHECKS=y by using `checked_sub`". I
> > was referring to the underflow check implicit in `new_len -
> > self.len()`.
>
> `checked_sub` always checks (if not optimized away). The config option
> is about the implicit one.
>
> Do you mean avoiding panics?

No, I meant avoiding the check. The existing code already explicitly
checks `new_len > self.len()` before evaluating `new_len -
self.len()`. This means the check occurs twice. `checked_sub` reduces
the number of checks by 1. Perhaps my wording could have been clearer
("avoid *an* underflow check").

Tamir