linux-kernel - Re: [PATCH 2/5] rust: time: Introduce Duration type

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Date: Tue, 26 Mar 2024 10:17:13 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>,
	Valentin Obst <kernel@...entinobst.de>
Subject: Re: [PATCH 2/5] rust: time: Introduce Duration type

On Tue, Mar 26, 2024 at 10:11:07AM -0700, Boqun Feng wrote:
[...]
> > > +impl Duration {
> > > +    /// Creates a new duration of `ns` nanoseconds.
> > > +    pub const fn new(ns: i64) -> Self {
> > > +        Self { inner: ns }
> > > +    }
> > > +
> > > +    /// Divides the number of nanoseconds by a compile-time constant.
> > > +    #[inline]
> > > +    fn divns_constant<const DIV: i64>(self) -> i64 {
> > > +        self.to_ns() / DIV
> > > +    }
> > 
> > I am a bit confused, why is this better than writing
> > `self.to_ns() / DIV` at the callsite?
> > 
> 
> Hmm.. you're right, there should be no difference I think. If there is
> nothing I'm missing from Alice, I will drop this function in the next
> version.
> 

On a second thought, I think this prevents accidentally divide a
non-const value, in other words, if you use this function, you're
guaranteed the divisor is a constant, and you have the compiler checking
that for you. So in that sense, I think it makes sense to remain it
here. Thoughts?

Regards,
Boqun

> Regards,
> Boqun
> 
> > -- 
> > Cheers,
> > Benno
> > 
> > > +
> > > +    /// Returns the number of milliseconds.
> > > +    #[inline]
> > > +    pub fn to_ms(self) -> i64 {
> > > +        self.divns_constant::<NSEC_PER_MSEC>()
> > > +    }
> > > +
> > > +    /// Returns the number of nanoseconds.
> > > +    #[inline]
> > > +    pub fn to_ns(self) -> i64 {
> > > +        self.inner
> > > +    }
> > > +}
> > > --
> > > 2.44.0
> > >