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

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Message-ID: <CAJ-ks9k+A1+0CWXZmD2m0+jRqTRTNFn-=d9VXqytiOqvn4BR0w@mail.gmail.com>
Date: Wed, 19 Mar 2025 09:42:33 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Andrew Ballance <andrewjballance@...il.com>, dakr@...nel.org, airlied@...il.com, 
	simona@...ll.ch, maarten.lankhorst@...ux.intel.com, mripard@...nel.org, 
	tzimmermann@...e.de, corbet@....net, ojeda@...nel.org, alex.gaynor@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu, 
	acourbot@...dia.com, nouveau@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 2/3] rust: alloc: add Vec::resize method

On Tue, Mar 18, 2025 at 8:50 PM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> On Tue Mar 18, 2025 at 9:12 PM CET, Tamir Duberstein wrote:
> > On Sun, Mar 16, 2025 at 7:17 AM Andrew Ballance
> > <andrewjballance@...il.com> wrote:
> >> +    pub fn resize(&mut self, new_len: usize, value: T, flags: Flags) -> Result<(), AllocError> {
> >> +        if new_len > self.len() {
> >> +            self.extend_with(new_len - self.len(), value, flags)
> >> +        } else {
> >> +            self.truncate(new_len);
> >> +            Ok(())
> >> +        }
> >> +    }
> >
> > You can avoid underflow checking in debug builds by using `checked_sub`:
>
> `checked_sub` doesn't only avoid underflow in debug builds, but rather
> in all builds. But the code below is a good suggestion.

Yes, I know :)

I included that language because the underflow check is likely
optimized away in release builds.

Tamir