| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
| 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 16:43:18 |
| Message-ID: | 8398.1577464998@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> On 2019-Dec-27, Tom Lane wrote:
>> ... 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
Yeah, I found that too. It looks promising, but we need to look into
* portability to different MSVC versions? (I guess the buildfarm would
tell us)
* performance, does it actually generate comparable code?
* intrinsics for the other bit instructions we use?
regards, tom lane
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