| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Nathan Bossart <nathandbossart(at)gmail(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Mats Kindahl <mats(at)timescale(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: glibc qsort() vulnerability |
| Date: | 2024-02-08 02:38:10 |
| Message-ID: | CA+hUKGLbC4O56rtFM69Tx6StT3PcVio9K2GisjZp=z6O20Q3sw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Feb 8, 2024 at 3:06 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2024-02-07 19:52:11 -0600, Nathan Bossart wrote:
> > On Wed, Feb 07, 2024 at 04:42:07PM -0800, Andres Freund wrote:
> > > On 2024-02-07 16:21:24 -0600, Nathan Bossart wrote:
> > >> The assembly for that looks encouraging, but I still need to actually test
> > >> it...
> > >
> > > Possible. For 16bit upcasting to 32bit is clearly the best way. For 32 bit
> > > that doesn't work, given the 32bit return, so we need something more.
> >
> > For the same compASC() test, I see an ~8.4% improvement with your int64
> > code
>
> Just to be clear, that code unfortuntely isn't correct, the return value is a
> 32 bit integer, so the 64bit difference doesn't help. In contrast to the 16bit
> case.
Perhaps you could wrap it in a branch-free sign() function so you get
a narrow answer?
https://stackoverflow.com/questions/14579920/fast-sign-of-integer-in-c
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