Re: [PATCH 2/2] rust: time: Implement basic arithmetic operations for Delta

[Alice Ryhl <aliceryhl@google.com>]

On Fri, Jul 25, 2025 at 10:20:08AM +0900, Alexandre Courbot wrote:
> On Fri Jul 25, 2025 at 3:54 AM JST, Lyude Paul wrote:
> > While rvkms is only going to be using a few of these, since Deltas are
> > basically the same as i64 it's easy enough to just implement all of the
> > basic arithmetic operations for Delta types.
> >
> > Note that for division and remainders, we currently limit these operations
> > to CONFIG_64BIT as u64 / u64 and u64 % u64 is not supported on all 32 bit
> > platforms natively. The correct solution we want to aim for here in the
> > future is to use the kernel's math library for performing these operations
> > so they're emulated on 32 bit platforms.
> >
> > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > ---
> >  rust/kernel/time.rs | 86 +++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 86 insertions(+)
> >
> > diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> > index ac5cab62070c6..8ece5a5d5a11b 100644
> > --- a/rust/kernel/time.rs
> > +++ b/rust/kernel/time.rs
> > @@ -251,6 +251,92 @@ pub struct Delta {
> >      nanos: i64,
> >  }
> >  
> > +impl ops::Add for Delta {
> > +    type Output = Self;
> > +
> > +    fn add(self, rhs: Self) -> Self {
> > +        Self {
> > +            nanos: self.nanos + rhs.nanos,
> 
> Should we use saturating ops here as well?

I'm not so sure ... I think it is useful for + to have the same meaning
always, and that meaning is "addition where overflow is a bug".

Alice