| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | John Naylor <john(dot)naylor(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: use CLZ instruction in AllocSetFreeIndex() |
| Date: | 2019-12-27 16:29:47 |
| Message-ID: | 20191227162947.GA25500@alvherre.pgsql |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On 2019-Dec-27, Tom Lane wrote:
> This kind of leads me to wonder if we don't need to expend more
> effort on the non-CLZ version of pg_leftmost_one_pos32; it seems
> like it shouldn't be losing this badly to the only-slightly-
> improved logic that's currently in AllocSetFreeIndex. On the
> other hand, the buildfarm thinks that __builtin_clz is essentially
> universal these days --- the only active non-MSVC critter that
> reports not having it is anole. So maybe it's not worth sweating
> over that. Perhaps what we really ought to be working on is
> finding MSVC equivalents for __builtin_clz and friends.
Apparently clz() can be written using _BitScanReverse(), per
https://stackoverflow.com/a/20468180
https://docs.microsoft.com/en-us/cpp/intrinsics/bitscanreverse-bitscanreverse64?view=vs-2015
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
| From | Date | Subject | |
|---|---|---|---|
| Next Message | David Fetter | 2019-12-27 16:37:28 | Re: use CLZ instruction in AllocSetFreeIndex() |
| Previous Message | Peter Eisentraut | 2019-12-27 16:25:58 | Remove libpq.rc, use win32ver.rc for libpq |