Re: UUID v7

On Fri, Nov 22, 2024 at 2:37 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Thu, Nov 21, 2024 at 1:22 PM Andrey M. Borodin <x4mmm@yandex-team.ru> wrote:
> >
> >
> >
> > > On 21 Nov 2024, at 02:24, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > >
> > >  But does replacing the least significant 2 bits
> > > with random 2 bits really not affect monotonicity?
> >
> > You are right. We have to take into account this when calculating monotonicity. PFA another version.
> >
>
> While it works fine, I think we need a comment for this change:
>
>  -#define SUB_MILLISECOND_STEP ((NS_PER_MS / (1 << 12)) + 1)
>  +#if defined(__darwin__) || _MSC_VER
>  +#define SUB_MILLISECOND_BITS 10
>  +#else
>  +#define SUB_MILLISECOND_BITS 12
>  +#endif
>  +#define SUB_MILLISECOND_STEP ((NS_PER_MS / (1 << SUB_MILLISECOND_BITS)) + 1)
>
> because the reader might think we should use SUB_MILLISECOND_BITS
> here too at a glance:
>
> +       /* sub-millisecond timestamp fraction (12 bits) */
> +       increased_clock_precision = ((ns % NS_PER_MS) * (1 << 12)) / NS_PER_MS;
>

I've attached an updated patch that squashed changes I made for v33.
We're still discussing increasing entropy on Windows and macOS, but
the patch seems to be in good shape.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com