Re: CC Mode with font-lock-maximum-decoration 2 [Was Major modes using `widen' is a good, even essential, programming practice.]

[Eli Zaretskii]

> Date: Mon, 8 Aug 2022 15:05:29 +0000
> Cc: emacs-devel@gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> For this measurement, I started with subr.el, and appended copies of it
> to itself, then took functions off the end, to make it the same size as
> xdisp.c.  xdisp.c is 1209233 bytes, my .el buffer was 1209371 bytes.
> 
> I used M-: (benchmark-run 1 (time-scroll-b)) on each buffer, with:
> 
>     (defun time-scroll-b (&optional arg)    ; For use in `benchmark-run'.
>       (condition-case nil
>           (while t
>             (if arg (scroll-down) (scroll-up))
>             (sit-for 0))
>         (error nil)))
> 
> ..  The exact results were:
> (xdisp.c): (5.7370774540000005 9 0.7672129740000013)
> (elisp):   (4.1201735589999995 5 0.42918214299999846).
> 
> This was, of course, on an optimised build on GNU/Linux using the Linux
> console, both measurements starting at BOB, having typed and deleted a
> character to erase existing font-locking.

Editing source code is more than just scrolling through the text and
getting it fontified, though.  For realistic measurements, you need to
emulate and time a typical mix of editing operations.