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Re: Processing speed in large C++ raw strings.

From: Tadeus Prastowo
Subject: Re: Processing speed in large C++ raw strings.
Date: Sat, 27 Apr 2019 17:35:16 +0200

Hi Alan,

On Sat, Apr 27, 2019 at 1:37 PM Alan Mackenzie <address@hidden> wrote:
> Hello, Tadeus.
> On Fri, Apr 26, 2019 at 22:15:28 +0200, Tadeus Prastowo wrote:
> > I have not made any report since I don't feel like sparing my time to
> > collect some data for the report now that switching to text-mode does
> > the trick.  So, since you are already at it, perhaps you may want to
> > find out why even scrolling the buffer in cc-mode is very slow when
> > visiting the file at
> > http://git.savannah.nongnu.org/cgit/tice.git/plain/tests/v1/test-v1_internals_program.cpp?
> You've submitted a bug report now.  :-)

I realize that now I have enough real data :-)

> > Specifically, I built master at commit
> > 82fc8ca6ba179596928db614ab903e44968ef44e and fired the result with
> > `emacs -Q' to visit the file locally.  Then, to experience the
> > sluggishness, I pressed M-> followed by M-v several times.  To further
> > experience it, I started to edit some template parameters, such as
> > changing `node1' to node `node5' in line 680.
> Thanks for drawing my attention to this problem with lots of templates.

My pleasure.  And, thank you very much for looking into this.

> The bug is that, in a certain low-level place, CC Mode was failing to
> mark the < and > "as parentheses" (with syntax-table text properties),
> hence a lot of unneeded buffer scanning was being done.
> The following patch should speed up the scrolling operation markedly.
> It does not become instantaneous, but takes a fraction of a second,
> compared with the several seconds it has taken up to now.  Would you
> please try it out.

I apply the following patch to master at commit
8dc00b2f1e6523c634df3e24379afbe712a32b27, and I confirm that the
following patch works to solve not only the buffer scrolling
sluggishness but also the template parameter editing sluggishness,
including the one that I sent to Stefan earlier today.  Thank you very
much, Alan, I really appreciate it.  Three lines of a diff to solve my
two-year old sluggishness problem.

> diff -r 1940f96b9799 cc-engine.el
> --- a/cc-engine.el      Fri Apr 26 01:01:07 2019 +0000
> +++ b/cc-engine.el      Sat Apr 27 11:30:06 2019 +0000
> @@ -5539,7 +5539,9 @@
>                       (prog1 (looking-at "\\s(")
>                         (forward-char))))
>           (backward-char)
> -         (if (c-forward-<>-arglist nil) ; Should always work.
> +         (if (let ((c-parse-and-markup-<>-arglists t)
> +                   (c-restricted-<>-arglists t))
> +               (c-forward-<>-arglist nil)) ; Should always work.
>               (when (> (point) to)
>                 (setq bound-<> (point)))
>             (forward-char)))

Best regards,

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