From: Stefan Monnier <monnier@iro.umontreal.ca>
To: emacs-devel@gnu.org
Subject: Re: [Emacs-diffs] master c66aaa6: Recomplexify ‘delete-trailing-whitespace’ by treating \n as whitespace again
Date: Wed, 15 Mar 2017 16:26:59 -0400 [thread overview]
Message-ID: <jwvinnap9vc.fsf-monnier+gmane.emacs.devel@gnu.org> (raw)
In-Reply-To: CAM-tV-9W1xPcwBmTZ9JGbKRuL6AKXR5E7OaFayGx-OLtCU+hLQ@mail.gmail.com
>>>>> Recomplexify ‘delete-trailing-whitespace’ by treating \n as
>>>>> whitespace again
>>>>> Mostly reverts "Simplify ‘delete-trailing-whitespace’ by not treating
>>>>> \n as whitespace" from 2016-07-04. Setting \n to non-whitespace
>>>>> causes the regex engine to backtrack a lot when searching for
>>>>> "\\s-+$" (Bug#26079).
>>>> Why do we use syntax-tables?
>>>> IOW why do we use \s- rather than something like [\s\t]?
>>> No clue. But (re-search-forward "[\s\t]+$" nil t) is also slow.
>> Slower than "\\s-+$"?
> No, seems to be twice as fast actually (this is still horribly slow).
I meant
slower than the best performance of "\\s-+$"?
because "[\s\t]+$" shouldn't backtrack. Using "\\s-+$" with
a syntax-table that puts \n in the whitespace syntax is indeed asking
for trouble, but I'm surprised "[\s\t]+$" is only twice as fast as this
pathological case (and hence presumably much slower than "\\s-+$" when
\n is not whitespace).
Stefan
next prev parent reply other threads:[~2017-03-15 20:26 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170315023157.29463.36647@vcs0.savannah.gnu.org>
[not found] ` <20170315023159.30AA520CAB@vcs0.savannah.gnu.org>
2017-03-15 11:28 ` [Emacs-diffs] master c66aaa6: Recomplexify ‘delete-trailing-whitespace’ by treating \n as whitespace again Stefan Monnier
2017-03-15 12:09 ` Noam Postavsky
2017-03-15 14:50 ` Stefan Monnier
2017-03-15 17:05 ` Noam Postavsky
2017-03-15 20:26 ` Stefan Monnier [this message]
2017-03-16 0:18 ` Noam Postavsky
2017-03-16 2:52 ` Stefan Monnier
2017-03-16 3:04 ` Noam Postavsky
2017-03-16 3:08 ` Stefan Monnier
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