From: Drew Adams <drew.adams@oracle.com>
To: Michael Heerdegen <michael_heerdegen@web.de>, help-gnu-emacs@gnu.org
Subject: RE: `looking-back' strange warning
Date: Thu, 1 Oct 2015 22:13:01 -0700 (PDT) [thread overview]
Message-ID: <ea2b4760-d658-4659-be98-dace8ae3a96b@default> (raw)
In-Reply-To: <877fn66pag.fsf@web.de>
> > You can pass (point-min) for the limit if that's what you want.
> > Making it optional Encourages people to think that looking-at is just
> > like looking-back, with the same performance characteristic, whereas
> > making it mandatory encourages people to put a reasonable limit and
> > hence avoid pathological behavior at the end of large buffers.
>
> My two cents: Even if you specify an optimal limit, `looking-back' can
> still be unnecessarily slow. For example,
> (looking-back "xy" 2)
> is much slower than
> (and (> (point) 2)
> (save-excursion (goto-char (- (point) 2))
> (looking-at "xy")))
> where "xy" stands for any plain string.
Definitely. And this is in fact a typical case of the
misuse: the string to check is often a literal, so its
length is known.
This is the first thing to mention about `looking-back',
in terms of performance: avoid it altogether, if you can.
next prev parent reply other threads:[~2015-10-02 5:13 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-30 8:25 `looking-back' strange warning Andreas Röhler
2015-10-01 6:20 ` Michael Heerdegen
2015-10-01 6:25 ` Tassilo Horn
2015-10-01 6:50 ` Dmitry Gutov
2015-10-01 7:49 ` Andreas Röhler
2015-10-01 8:20 ` Tassilo Horn
2015-10-01 8:46 ` Andreas Röhler
2015-10-01 9:29 ` Tassilo Horn
2015-10-02 0:10 ` Stefan Monnier
2015-10-02 15:21 ` Tassilo Horn
2015-10-01 16:00 ` Drew Adams
2015-10-01 17:56 ` Dmitry Gutov
2015-10-01 18:24 ` Andreas Röhler
2015-10-01 18:59 ` Dmitry Gutov
2015-10-01 19:55 ` Andreas Röhler
2015-10-01 20:26 ` Dmitry Gutov
2015-10-02 0:15 ` Stefan Monnier
2015-10-02 1:18 ` Michael Heerdegen
2015-10-02 5:13 ` Drew Adams [this message]
2015-10-02 20:28 ` Drew Adams
2015-10-02 20:59 ` Tassilo Horn
2015-10-02 21:35 ` Drew Adams
2015-10-03 6:26 ` Tassilo Horn
2015-10-03 6:45 ` Andreas Röhler
2015-10-03 15:20 ` Drew Adams
2015-10-03 15:17 ` Drew Adams
2015-10-02 1:19 ` Michael Heerdegen
2015-10-02 5:12 ` Drew Adams
2015-10-02 6:16 ` Andreas Röhler
2015-10-02 6:36 ` Michael Heerdegen
2015-10-02 12:46 ` Stefan Monnier
2015-10-02 15:02 ` Drew Adams
2015-10-02 19:08 ` Tom Tromey
2015-10-02 19:33 ` Stefan Monnier
2015-10-03 18:11 ` Stefan Monnier
[not found] ` <mailman.176.1443721449.16064.help-gnu-emacs@gnu.org>
2015-10-01 18:50 ` Barry Margolin
[not found] ` <<barmar-D40496.14502501102015@88-209-239-213.giganet.hu>
2015-10-01 23:42 ` Drew Adams
2015-10-02 0:12 ` Stefan Monnier
2015-10-02 5:10 ` Drew Adams
2015-10-02 12:48 ` Stefan Monnier
2015-10-02 15:03 ` Drew Adams
2015-10-02 15:21 ` Stefan Monnier
2015-10-02 15:24 ` Drew Adams
2015-10-02 19:28 ` Stefan Monnier
2015-10-01 12:35 ` Artur Malabarba
[not found] <<560B9C7F.2060301@easy-emacs.de>
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