Re: State of the overlay tree branch?

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: emacs-devel@gnu.org
> Date: Mon, 19 Mar 2018 08:29:40 -0400
> 
> > But I don't believe [display_count_lines] could be orders of
> > magnitude faster than count-lines, even though it doesn't need to
> > convert character position to byte position.
> 
> Scanning from the last used position can be *very* different from
> scanning from point-min.  So yes, it can be orders of magnitude faster

Well, in my measurements it's already very fast.  I don't understand
why the OP sees times that are 10 times slower.

> The
> 
>   for (tail = BUF_MARKERS (b); tail; tail = tail->next)
> 
> loop in buf_charpos_to_bytepos and buf_bytepos_to_charpos.
> 
> > But find_newline doesn't look for markers, and it converts character
> > to byte position just 2 times.  Or am I missing something?
> 
> The idea is that the above loop (even if called only twice) might be
> sufficient to make line-number-at-pos take 0.2s.

I very much doubt that loop could take such a long time.  And running
a benchmark 1000 times means that the 2nd through 1000th iteration
find the mapping much faster, probably bypassing the loop entirely.

> So for them to cause the slow down seen here, we'd need not only
> a very large number of markers but also additional conditions that might
> not be very likely.
> But it's still a possibility.

I'll believe it when I see it.