(Faset): Fix previous change.

1 files changed, 12 insertions, 14 deletions

diff --git a/src/data.c b/src/data.c
index da9d86f81bc..bed8bda7b7c 100644
--- a/src/data.c
+++ b/src/data.c
@@ -1853,8 +1853,8 @@ IDX starts at 0.")
   else if (STRING_MULTIBYTE (array))
     {
       int c, idxval_byte, new_len, actual_len;
+      int prev_byte;
       unsigned char *p, workbuf[4], *str;
-      int recount = 0;
 
       if (idxval < 0 || idxval >= XSTRING (array)->size)
         args_out_of_range (array, idx);
@@ -1862,25 +1862,23 @@ IDX starts at 0.")
       idxval_byte = string_char_to_byte (array, idxval);
       p = &XSTRING (array)->data[idxval_byte];
 
-      actual_len
-        = MULTIBYTE_FORM_LENGTH (p, STRING_BYTES (XSTRING (array)) - idxval_byte);
+      actual_len = MULTIBYTE_FORM_LENGTH (p, STRING_BYTES (XSTRING (array)));
       CHECK_NUMBER (newelt, 2);
       new_len = CHAR_STRING (XINT (newelt), workbuf, str);
       if (actual_len != new_len)
         error ("Attempt to change byte length of a string");
-      if (!CHAR_HEAD_P (*str)
-          || !CHAR_HEAD_P (XSTRING (array)->data[idxval_byte + actual_len]))
-        /* We may have to combine bytes.  */
-        recount = 1;
+
+      /* We can't accept a change causing byte combining.  */
+      if ((idxval > 0 && !CHAR_HEAD_P (*str)
+           && (prev_byte = string_char_to_byte (array, idxval - 1),
+               (prev_byte + 1 < idxval_byte
+                || (p[-1] >= 0x80 && p[-1] < 0xA0))))
+          || (idxval < XSTRING (array)->size - 1
+              && (*str >=0x80 && *str < 0xA0)
+              && !CHAR_HEAD_P (p[actual_len])))
+        error ("Attempt to change char length of a string");
       while (new_len--)
         *p++ = *str++;
-      if (recount)
-        {
-          XSTRING (array)->size =
-            chars_in_text (XSTRING (array)->data,
-                           STRING_BYTES (XSTRING (array)));
-          clear_string_char_byte_cache ();
-        }
     }
   else
     {