Re: UUID v7

On 10.03.24 13:59, Andrey M. Borodin wrote:
>> The functions uuid_extract_ver and uuid_extract_var could be named
>> uuid_extract_version and uuid_extract_variant. Otherwise, it's hard
>> to tell them apart, with only one letter different.
>
> Renamed.

Another related comment: Throughout your patch, swap the order of
uuid_extract_variant and uuid_extract_version. First, this makes more
sense because version is subordinate to variant, and also it makes it
alphabetical.

>> I think the behavior of uuid_extract_var(iant) is wrong. The code
>> takes just two bits to return, but the draft document is quite clear
>> that the variant is 4 bits (see Table 1).
>
> Well, it was correct only for implemented variant. I've made version that implements full table 1 from section 4.1.

I think we are still interpreting this differently. I think
uuid_extract_variant should just return whatever is in those four bits.
Your function comment says "Can return only 0, 0b10, 0b110 and 0b111.",
which I don't think it is correct. It should return 0 through 15.

>> I would have expected that, since gettimeofday() provides microsecond
>> precision, we'd put the extra precision into "rand_a" as per Section 6.2 method 3.
>
> I had chosen method 2 over method 3 as most portable. Can we be sure how many bits (after reading milliseconds) are there across different OSes?

I think this should have been researched. If we don't know how many
bits we have, how do we know we have enough for milliseconds? I think
we should at least have some kind of idea, if we are going to have this
conversation.