From: Paul Eggert <eggert@cs.ucla.edu>
To: Dmitry Antipov <dmantipov@yandex.ru>
Cc: 18361@debbugs.gnu.org
Subject: bug#18361: New 'sort' implementation can crash Emacs
Date: Fri, 29 Aug 2014 16:07:09 -0700 [thread overview]
Message-ID: <5401079D.7070505@cs.ucla.edu> (raw)
In-Reply-To: <540102E5.6040404@yandex.ru>
Dmitry Antipov wrote:
> Can you provide an example?
Sure, a comparison function that returns a new random value every time
you call it. Such a function is most likely not well formed, that is,
it most likely does not define a total order.
> Is that just a poor property of the particular qsort(_r) implementation?
Yes and no. qsort is allowed to have undefined behavior (what you're
calling a "poor property") if given a comparison function that is not a
total order; see
<http://pubs.opengroup.org/onlinepubs/9699919799/functions/qsort.html>
DESCRIPTION paragraph 4. Perhaps some qsort implementations have well
defined behavior in this case (and so don't have the "poor property"),
but there are performance reasons for qsort to have the "poor property"
and in my experience most implementations have it. GNU qsort and
qsort_r, for example, have the "poor property".
next prev parent reply other threads:[~2014-08-29 23:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-29 21:24 bug#18361: New 'sort' implementation can crash Emacs Paul Eggert
2014-08-29 22:47 ` Dmitry Antipov
2014-08-29 23:07 ` Paul Eggert [this message]
2014-08-30 5:07 ` Dmitry Antipov
2014-08-30 5:22 ` Paul Eggert
2014-08-30 6:55 ` Dmitry Antipov
2014-08-30 13:44 ` Paul Eggert
2014-08-30 23:05 ` Paul Eggert
2014-08-31 2:50 ` Eli Zaretskii
2014-08-31 4:46 ` Paul Eggert
2014-08-31 15:20 ` Eli Zaretskii
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