Re: [PATCH v6 01/38] minmax: Add in_range() macro

[Phi Nguyen]

On 8/3/2023 9:22 PM, Matthew Wilcox wrote:
> On Thu, Aug 03, 2023 at 09:00:35PM +0800, Phi Nguyen wrote:
> > On 8/2/2023 11:13 PM, Matthew Wilcox (Oracle) wrote:
> > > +static inline bool in_range64(u64 val, u64 start, u64 len)
> > > +{
> > > +	return (val - start) < len;
> > > +}
> > > +
> > > +static inline bool in_range32(u32 val, u32 start, u32 len)
> > > +{
> > > +	return (val - start) < len;
> > > +}
> > > +
> >
> > I think these two functions return wrong result if val is smaller than start
> > and len is big enough.
>
> How is it that you stopped reading at exactly the point where I explained
> that this is intentional?
>
> +/**
> + * in_range - Determine if a value lies within a range.
> + * @val: Value to test.
> + * @start: First value in range.
> + * @len: Number of values in range.
> + *
> + * This is more efficient than "if (start <= val && val < (start + len))".
> + * It also gives a different answer if @start + @len overflows the size of
> + * the type by a sufficient amount to encompass @val.  Decide for yourself
> + * which behaviour you want, or prove that start + len never overflow.
> + * Do not blindly replace one form with the other.
> + */

Oh, sorry, I see, my bad.