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I really like the package sml-modeline (it is available on melpa): https://melpa.org/#/sml-modeline With it I replaced my vertical scrollbars.

But when opening large text files like this Raspbian-Package-List (warning: 38MB download) then Emacs gets realy slow. Disabling sml-modeline-mode instantly speeds up emacs.

So I had a look at sml-modelines source code. In function sml-modeline-create there is a call to widen and point-max, which I suspect to make sml-modeline-mode so slow (*1*).

If (*1*) is the case, is it possible to store those values in between calls of sml-modeline-create to speed things up, and how do it? I think those values need to be stored for every single buffer, or every time a call to switch-to-buffer is done.

If (*1*) is not the case, what operations make sml-modeline-mode so slow and how to speed this up?

This Package did not get an update since January 2012, so maybe it is already abandoned. :-(

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  • The slow-down is due to line-number-at-pos that is called in a few places. For a fix/workaround, see this related thread entitled "A faster method to obtain line-number-at-pos in large buffers": emacs.stackexchange.com/questions/3821/… You may also wish to tell the author about this problem and workaround/fix. Essentially, you can use (save-excursion (goto-char ...)) with the answer by Constantine in the related thread. Commented Jun 12, 2017 at 23:47
  • @lawlist wow it is working. :) One need to replace (setq number-max (line-number-at-pos (point-max))) (setq number-beg (line-number-at-pos wstart)) (setq number-end (line-number-at-pos wend))) with (save-excursion (goto-char (point-max)) (setq number-max (string-to-number (format-mode-line "%l"))) (goto-char wstart) (setq number-beg (string-to-number (format-mode-line "%l"))) (goto-char wstart) (setq number-end (string-to-number (format-mode-line "%l"))))) if you write a answer I will accept it. Thank you! Commented Jun 13, 2017 at 0:25

2 Answers 2

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The slow-down is caused by calls to line-number-at-pos. As mentioned in the answer by username Constantine in the related thread entitled "A faster method to obtain line-number-at-pos in large buffers" https://emacs.stackexchange.com/a/3822/2287, (string-to-number (format-mode-line "%l")) can be used to expeditiously extract the line number from a buffer that is visible. There are a few exceptions discussed in the answer and comments of the aforementioned thread that are certainly worth reading.

The general way to apply this approach is by using (save-excursion (goto-char ...) (string-to-number (format-mode-line "%l"))). If a string instead of a raw number is desired, then just remove the string-to-number statement from the above snippet.

The original poster has commented underneath the question applying this approach to the specific fact pattern of sml-modeline; however, @lawlist has not done any testing with said library and is unable to post a specific answer in relation thereto.

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Just in case the author of sml-modeline is not updating, here a step by step guide:

1.) open sml-modeline.el from your install directory
(probably: ~/.emacs.d/elpa/sml-modeline-20120110.1240/sml-modeline.el)

2.) goto line 139 of the file and replace lines 

 (setq number-max (line-number-at-pos (point-max))) (setq number-beg (line-number-at-pos wstart)) (setq number-end (line-number-at-pos wend)))

with:

(save-excursion (goto-char (point-max)) (setq number-max (string-to-number (format-mode-line "%l"))) (goto-char wstart) (setq number-beg (string-to-number (format-mode-line "%l"))) (goto-char wstart) (setq number-end (string-to-number (format-mode-line "%l")))))

3.) save and do M-x byte-compile-file
4.) restart emacs

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