bug#46933: Possible bugs in filepos-to-bufferpos / bufferpos-to-filepos

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Eli Zaretskii <eliz@gnu.org>,  gregory@heytings.org,  46933@debbugs.gnu.org
> Date: Mon, 20 Jun 2022 02:59:52 +0200
> 
> handa <handa@gnu.org> writes:
> 
> > For the latter case, perhaps something like the following code works.
> >
> > ;; Return the buffer position correspoinding to the byte position
> > ;; FILEPOS in FILE provided that FILE is decoded by CODING-SYSTEM.
> > (defun temp (file filepos coding-system)
> >   (with-temp-buffer
> >     (set-buffer-multibyte nil)
> >     (insert-file-contents-literally file)
> >     (let ((full (decode-coding-region 1 (point-max) coding-system t))
> > 	  partial)
> >       (while (and (setq partial (decode-coding-region 1 (1+ filepos)
> > 						      coding-system t))
> > 		  (not (eq (compare-strings full 0 (length partial)
> > 					    partial 0 (length partial))
> > 			   t)))
> > 	  (setq filepos (1+ filepos)))
> >       (1+ (length partial)))))
> >
> > If it is too slow, there are a few ways to make it faster.
> 
> (I'm going through old bug reports that unfortunately weren't resolved
> at the time.)
> 
> If I understand correctly, the suggestion here is to use this function
> in Info-find-node-2 instead of `filepos-to-bufferpos'?

"Unless it's too slow".