GNU bug report logs - #77924
31.0.50; [Feature branch] Change marker implementation

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Gerd Möllmann <gerd.moellmann <at> gmail.com>
Cc: Eli Zaretskii <eliz <at> gnu.org>, stefankangas <at> gmail.com, 77924 <at> debbugs.gnu.org
Subject: bug#77924: 31.0.50; [Feature branch] Change marker implementation
Date: Sat, 26 Apr 2025 19:19:52 -0400

> -  /* Don't scan forward if CHARPOS is exactly on the previous known
> -     position because the index bytepos can be in the middle of a
> -     character, which is found by scanning backwards.  */
> -  ptrdiff_t bytepos
> -    = (charpos == prev.charpos ? bytepos_of_head (b, prev.bytepos)
> -       : (charpos - prev.charpos < next.charpos - charpos
> -	  ? bytepos_forward_to_charpos (b, prev, charpos)
> -	  : bytepos_backward_to_charpos (b, next, charpos)));
> +  /* Scan forward if the distance to the previous known position is
> +     smaller than the distance to the next known position.  */
> +  const ptrdiff_t bytepos
> +    = (charpos - prev.charpos < next.charpos - charpos
> +       ? bytepos_forward_to_charpos (b, prev, charpos)
> +       : bytepos_backward_to_charpos (b, next, charpos));

I don't understand: `prev` can point into the middle of a char, so if
`charpos == prev.charpos`, `bytepos_forward_to_charpos` may return an
incorrect `bytepos` (it'll return `prev.bytepos` which can be in the
middle of that char).


        Stefan

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