| From: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
|---|---|
| To: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, 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 02:56:20 |
| Message-ID: | 20240208025620.GC445153@nathanxps13 |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On Thu, Feb 08, 2024 at 03:49:03PM +1300, Thomas Munro wrote:
> On Thu, Feb 8, 2024 at 3:38 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
>> 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
>
> Ah, strike that, it is much like the suggested (a > b) - (a < b) but
> with extra steps...
Yeah, https://godbolt.org/ indicates that the sign approach compiles to
movsx rsi, esi
movsx rdi, edi
xor eax, eax
sub rdi, rsi
test rdi, rdi
setg al
shr rdi, 63
sub eax, edi
ret
while the approach Andres suggested compiles to
xor eax, eax
cmp edi, esi
setl dl
setg al
movzx edx, dl
sub eax, edx
ret
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Hayato Kuroda (Fujitsu) | 2024-02-08 03:04:05 | RE: speed up a logical replica setup |
| Previous Message | Tom Lane | 2024-02-08 02:53:02 | Re: cfbot is failing all tests on FreeBSD/Meson builds |