Fix access to single-byte characters in buffer text

* src/xdisp.c (get_visually_first_element)
(Fbidi_find_overridden_directionality):
* src/cmds.c (Fend_of_line): Use FETCH_BYTE instead of FETCH_CHAR,
and byte position instead of character position, to access
individual bytes of buffer text.  This avoids producing invalid
characters and accessing wrong buffer positions.  (Bug#41520)

2 files changed, 5 insertions, 5 deletions

diff --git a/src/cmds.c b/src/cmds.c
index 5d7a45e65f6..9914b7a01f7 100644
--- a/src/cmds.c
+++ b/src/cmds.c
@@ -203,7 +203,7 @@ to t.  */)
       SET_PT (newpos);
 
       if (PT > newpos
-          && FETCH_CHAR (PT - 1) == '\n')
+          && FETCH_BYTE (PT_BYTE - 1) == '\n')
         {
           /* If we skipped over a newline that follows
              an invisible intangible run,
@@ -214,7 +214,7 @@ to t.  */)
           break;
         }
       else if (PT > newpos && PT < ZV
-               && FETCH_CHAR (PT) != '\n')
+               && FETCH_BYTE (PT_BYTE) != '\n')
         /* If we skipped something intangible
            and now we're not really at eol,
            keep going.  */
diff --git a/src/xdisp.c b/src/xdisp.c
index 1e865898e37..bff6218106b 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -8264,8 +8264,8 @@ get_visually_first_element (struct it *it)
     }
   else if (it->bidi_it.charpos == bob
            || (!string_p
-               && (FETCH_CHAR (it->bidi_it.bytepos - 1) == '\n'
-                   || FETCH_CHAR (it->bidi_it.bytepos) == '\n')))
+               && (FETCH_BYTE (it->bidi_it.bytepos - 1) == '\n'
+                   || FETCH_BYTE (it->bidi_it.bytepos) == '\n')))
     {
       /* If we are at the beginning of a line/string, we can produce
          the next element right away.  */
@@ -24157,7 +24157,7 @@ the `bidi-class' property of a character.  */)
           itb.charpos = BEGV;
           itb.bytepos = BEGV_BYTE;
         }
-      else if (FETCH_CHAR (from_bpos - 1) == '\n')
+      else if (FETCH_BYTE (from_bpos - 1) == '\n')
         {
           itb.charpos = from_pos;
           itb.bytepos = from_bpos;