On Wed, Mar 19, 2025 at 12:06?PM Miguel Ojeda
<miguel.ojeda.sandonis at gmail.com> wrote:>
> On Wed, Mar 19, 2025 at 4:59?PM Tamir Duberstein <tamird at
gmail.com> 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