Re: Inconsistent results with libc sorting on Windows

On Wed, Jun 14, 2023 at 4:13 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:

> On Tue, Jun 13, 2023 at 5:59 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
> wrote:
> > Trying to follow along here... you're doing the moral equivalent of
> > strxfrm(), so sort keys have the transitive property but direct string
> > comparisons don't? Or is this because LCIDs reach a different
> > algorithm somehow (or otherwise why do you need to use LCIDs for this,
> > when there is a non-LCID version of that function, with a warning not
> > to use the older LCID version[1]?)
>
> I'm reminded of the fact that the abbreviated keys strxfrm() debacle
> (back when 9.5 was released) was caused by a bug in strcoll() -- not a
> bug in strxfrm() itself. From our point of view the problem was that
> strxfrm() failed to be bug compatible with strcoll() due to a buggy
> strcoll() optimization.
>
> I believe that strxfrm() is generally less likely to have bugs than
> strcoll(). There are far fewer opportunities to dodge unnecessary work
> in the case of strxfrm()-like algorithms (offering something like
> ICU's pg_strnxfrm_prefix_icu() prefix optimization is the only one).
> On the other hand, collation library implementers are likely to
> heavily optimize strcoll() for typical use-cases such as sorting and
> binary search. Using strxfrm() for everything is discouraged [1].
>

Yes, I think the situation is quite similar to what you describe, with its
WIN32 peculiarities. Take for example the attached program, it'll output:

s1 = s2
s2 = s3
s1 > s3
c1 > c2
c2 > c3
c1 > c3

As you can see the test for CompareStringEx() is broken, but we get a sane
answer with LCMapStringEx().

Regards,

Juan José Santamaría Flecha