From: "René Scharfe" <l.s.r@web.de>
To: Kevin Bracey <kevin@bracey.fi>, GIT Mailing-list <git@vger.kernel.org>
Subject: Re: [PATCH 1/3] add QSORT
Date: Tue, 4 Oct 2016 00:00:10 +0200 [thread overview]
Message-ID: <9ff725eb-3536-638b-1ec0-ff9130478abc@web.de> (raw)
In-Reply-To: <57F290DC.5080303@bracey.fi>
Am 03.10.2016 um 19:09 schrieb Kevin Bracey:
> As such, NULL checks can still be elided even with your change. If you
> effectively change your example to:
>
> if (nmemb > 1)
> qsort(array, nmemb, size, cmp);
> if (!array)
> printf("array is NULL\n");
>
> array may only be checked for NULL if nmemb <= 1. You can see GCC doing
> that in the compiler explorer - it effectively turns that into "else
> if".
We don't support array == NULL together with nmemb > 1, so a segfault is
to be expected in such cases, and thus NULL checks can be removed safely.
> To make that check really work, you have to do:
>
> if (array)
> qsort(array, nmemb, size, cmp);
> else
> printf("array is NULL\n");
>
> So maybe your "sane_qsort" should be checking array, not nmemb.
It would be safe, but arguably too much so, because non-empty arrays
with NULL wouldn't segfault anymore, and thus become harder to identify
as the programming errors they are.
The intention is to support NULL pointers only for empty arrays (in
addition to valid pointers). That we also support NULL pointers for
arrays with a single member might be considered to be the result of a
premature optimization, but it should be safe -- the compiler won't
remove checks unexpectedly.
Does that make sense (it's getting late here, so my logic might already
be resting..)?
René
next prev parent reply other threads:[~2016-10-03 22:00 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-29 15:23 [PATCH 1/3] add QSORT René Scharfe
2016-09-29 15:27 ` [PATCH 2/3] use QSORT René Scharfe
2016-09-29 15:29 ` [PATCH 3/3] remove unnecessary check before QSORT René Scharfe
2016-09-29 22:36 ` [PATCH 1/3] add QSORT Junio C Hamano
2016-09-29 23:21 ` René Scharfe
2016-09-29 23:40 ` René Scharfe
2016-10-01 16:19 ` René Scharfe
2016-10-03 16:46 ` Kevin Bracey
2016-10-03 17:09 ` Kevin Bracey
2016-10-03 22:00 ` René Scharfe [this message]
2016-10-04 5:28 ` Kevin Bracey
2016-10-04 20:31 ` René Scharfe
2016-10-05 15:00 ` Kevin Bracey
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=9ff725eb-3536-638b-1ec0-ff9130478abc@web.de \
--to=l.s.r@web.de \
--cc=git@vger.kernel.org \
--cc=kevin@bracey.fi \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).