From: Alejandro Colomar <alx.manpages@gmail.com>
To: Noah Goldstein <goldstein.w.n@gmail.com>
Cc: Wilco Dijkstra <Wilco.Dijkstra@arm.com>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH 1/1] string: Add stpecpy(3)
Date: Tue, 27 Dec 2022 00:24:53 +0100 [thread overview]
Message-ID: <1de69fc6-592f-70f5-e318-1a2e8efa651c@gmail.com> (raw)
In-Reply-To: <b0c699a7-c918-a5bd-e1c3-66977291ece0@gmail.com>
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On 12/26/22 23:25, Alejandro Colomar wrote:
> Hi Noah,
>
> On 12/26/22 03:43, Noah Goldstein wrote:
>
>> I see. The code you commented earlier was NULL for both.
>
> I don't remember; maybe there was a typo...
>
>>
>> Either way you can just make it:
>>
>> ```
>> if((dst - 1UL) >= (end - 1UL)) {
>
> I didn't expect that would be significantly better than `(dst == end || dst ==
> NULL)`. However, I compiled both just to see, and the assembly output for your
> code is shorter. I'll benchmark both to see if there are performance differences.
>
> I wonder why the compiler doesn't generate this code if it's better; it has all
> the information to decide that it can be transformed into that.
>
> Both clang and GCC produce better code with your suggestion (although in the
> case of GCC, the difference is bigger.
Self-correction:
They produce smaller code for your suggestion, but it seems to be slower code.
>
> Cheers,
>
> Alex
>
>> return dst; // either dst == NULL or dst == end.
>> }
>> ```
>
>
--
<http://www.alejandro-colomar.es/>
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next prev parent reply other threads:[~2022-12-26 23:25 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-23 23:24 Wilco Dijkstra
2022-12-24 0:05 ` Alejandro Colomar
2022-12-24 0:26 ` Alejandro Colomar
2022-12-24 2:30 ` stpecpy(3) vs strlcpy(3) benchmark (was: [PATCH 1/1] string: Add stpecpy(3)) Alejandro Colomar
2022-12-24 10:28 ` Alejandro Colomar
2022-12-25 1:52 ` [PATCH 1/1] string: Add stpecpy(3) Noah Goldstein
2022-12-25 14:37 ` Alejandro Colomar
2022-12-25 22:31 ` Noah Goldstein
2022-12-26 0:26 ` Alejandro Colomar
2022-12-26 0:32 ` Noah Goldstein
2022-12-26 0:37 ` Alejandro Colomar
2022-12-26 2:43 ` Noah Goldstein
2022-12-26 22:25 ` Alejandro Colomar
2022-12-26 23:24 ` Alejandro Colomar [this message]
2022-12-26 23:52 ` Alejandro Colomar
2022-12-27 0:12 ` Alejandro Colomar
-- strict thread matches above, loose matches on Subject: below --
2022-12-23 18:35 Wilco Dijkstra
2022-12-23 22:40 ` Alejandro Colomar
2022-12-23 14:59 Wilco Dijkstra
2022-12-23 17:03 ` Alejandro Colomar
2022-12-23 17:27 ` Alejandro Colomar
2022-12-22 21:42 [PATCH 0/1] " Alejandro Colomar
2022-12-22 21:42 ` [PATCH 1/1] " Alejandro Colomar
2022-12-23 7:02 ` Sam James
2022-12-23 12:26 ` Alejandro Colomar
2022-12-23 12:29 ` Alejandro Colomar
2022-12-23 17:21 ` Alejandro Colomar
2022-12-31 15:13 ` Sam James
2022-12-31 15:15 ` Alejandro Colomar
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