Re: A qsort template

Hi,

For 0001-Add-bsearch-and-unique-templates-to-sort_template.h.patch :

+ * Remove duplicates from an array. Return the new size.
+ */
+ST_SCOPE size_t
+ST_UNIQUE(ST_ELEMENT_TYPE *array,

The array is supposed to be sorted, right ?
The comment should mention this.

Cheers

On Sat, Mar 13, 2021 at 6:36 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:

> On Sat, Mar 13, 2021 at 3:49 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
> wrote:
> > On Fri, Mar 12, 2021 at 7:58 AM Andres Freund <andres(at)anarazel(dot)de>
> wrote:
> > > I wish we had the same for bsearch... :)
> >
> > Glibc already has the definition of the traditional void-based
> > function in /usr/include/bits/stdlib-bsearch.h, so the generated code
> > when the compiler can see the comparator definition is already good in
> > eg lazy_tid_reaped() and eg some nbtree search routines. We could
> > probably expose more trivial comparators in headers to get more of
> > that, and we could perhaps put our own bsearch definition in a header
> > for other platforms that didn't think of that...
> >
> > It might be worth doing type-safe macro templates as well, though (as
> > I already did in an earlier proposal[1]), just to have nice type safe
> > code though, not sure, I'm thinking about that...
>
> I remembered a very good reason to do this: the ability to do
> branch-free comparators in more places by introducing optional wider
> results. That's good for TIDs (needs 49 bits), and places that want
> to "reverse" a traditional comparator (just doing -result on an int
> comparator that might theoretically return INT_MIN requires at least
> 33 bits). So I rebased the relevant parts of my earlier version, and
> went through and wrote a bunch of examples to demonstrate all this
> stuff actually working.
>
> There are two categories of change in these patches:
>
> 0002-0005: Places that sort/unique/search OIDs, BlockNumbers and TIDs,
> which can reuse a small set of typed functions (a few more could be
> added, if useful). See sortitemptr.h and sortscalar.h. Mostly this
> is just a notational improvement, and an excuse to drop a bunch of
> duplicated code. In a few places this might really speed something
> important up! Like VACUUM's lazy_tid_reaped().
>
> 0006-0009. Places where a specialised function is generated for one
> special purpose, such as ANALYZE's HeapTuple sort, tidbitmap.c's
> pagetable sort, some places in nbtree code etc. These may require
> some case-by-case research on whether the extra executable size is
> worth the speedup, and there are surely more opportunities like that;
> I just picked on these arbitrarily.
>