Widen modiff counts to avoid wraparound

Widen modification counts to at least 64 bits, to make
wraparound practically impossible.
* doc/lispref/buffers.texi (Buffer Modification):
Don’t say the modification-count can wrap around.
* src/buffer.c (Frestore_buffer_modified_p, Fbuffer_swap_text)
(modify_overlay):
* src/insdel.c (insert_1_both, insert_from_string_1)
(insert_from_gap, insert_from_buffer_1)
(adjust_after_replace, replace_range, replace_range_2)
(del_range_2, modify_text):
* src/textprop.c (modify_text_properties):
Use modiff_incr instead of incrementing	directly.
(Fbuffer_modified_tick, Fbuffer_chars_modified_tick):
Don’t assume modification counts fit into fixnums.
* src/buffer.h (struct buffer_text, struct buffer):
* src/cmds.c (internal_self_insert):
* src/fileio.c (Finsert_file_contents):
* src/indent.c (last_known_column_modified):
* src/keyboard.c (command_loop_1):
* src/marker.c (cached_modiff):
* src/syntax.c (find_start_modiff, parse_sexp_propertize)
(find_defun_start):
* src/window.h (struct window):
Use modiff_count for modification counts.
* src/editfns.c (Fsubst_char_in_region):
Copy instead of incrementing modification counts,
since integer overflow checking is not needed here.
* src/lisp.h (modiff_count): New type.
(modiff_incr, modiff_to_integer): New inline functions.
* src/pdumper.c (dump_buffer): Update hash.

1 files changed, 14 insertions, 11 deletions

diff --git a/src/buffer.c b/src/buffer.c
index a12c80ec0b0..e5cc5f367f0 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1413,7 +1413,7 @@ state of the current buffer.  Use with care.  */)
                  /* If SAVE_MODIFF == auto_save_modified == MODIFF,
                     we can either decrease SAVE_MODIFF and auto_save_modified
                     or increase MODIFF.  */
-                 : MODIFF++);
+                 : modiff_incr (&MODIFF));
 
   return flag;
 }
@@ -1422,11 +1422,11 @@ DEFUN ("buffer-modified-tick", Fbuffer_modified_tick, Sbuffer_modified_tick,
        0, 1, 0,
        doc: /* Return BUFFER's tick counter, incremented for each change in text.
 Each buffer has a tick counter which is incremented each time the
-text in that buffer is changed.  It wraps around occasionally.
-No argument or nil as argument means use current buffer as BUFFER.  */)
-  (register Lisp_Object buffer)
+text in that buffer is changed.  No argument or nil as argument means
+use current buffer as BUFFER.  */)
+  (Lisp_Object buffer)
 {
-  return make_fixnum (BUF_MODIFF (decode_buffer (buffer)));
+  return modiff_to_integer (BUF_MODIFF (decode_buffer (buffer)));
 }
 
 DEFUN ("buffer-chars-modified-tick", Fbuffer_chars_modified_tick,
@@ -1439,9 +1439,9 @@ values returned by two individual calls of `buffer-chars-modified-tick',
 you can tell whether a character change occurred in that buffer in
 between these calls.  No argument or nil as argument means use current
 buffer as BUFFER.  */)
-  (register Lisp_Object buffer)
+  (Lisp_Object buffer)
 {
-  return make_fixnum (BUF_CHARS_MODIFF (decode_buffer (buffer)));
+  return modiff_to_integer (BUF_CHARS_MODIFF (decode_buffer (buffer)));
 }
 
 DEFUN ("rename-buffer", Frename_buffer, Srename_buffer, 1, 2,
@@ -2375,9 +2375,12 @@ results, see Info node `(elisp)Swapping Text'.  */)
   bset_point_before_scroll (current_buffer, Qnil);
   bset_point_before_scroll (other_buffer, Qnil);
 
-  current_buffer->text->modiff++;         other_buffer->text->modiff++;
-  current_buffer->text->chars_modiff++;   other_buffer->text->chars_modiff++;
-  current_buffer->text->overlay_modiff++; other_buffer->text->overlay_modiff++;
+  modiff_incr (&current_buffer->text->modiff);
+  modiff_incr (&other_buffer->text->modiff);
+  modiff_incr (&current_buffer->text->chars_modiff);
+  modiff_incr (&other_buffer->text->chars_modiff);
+  modiff_incr (&current_buffer->text->overlay_modiff);
+  modiff_incr (&other_buffer->text->overlay_modiff);
   current_buffer->text->beg_unchanged = current_buffer->text->gpt;
   current_buffer->text->end_unchanged = current_buffer->text->gpt;
   other_buffer->text->beg_unchanged = other_buffer->text->gpt;
@@ -3913,7 +3916,7 @@ modify_overlay (struct buffer *buf, ptrdiff_t start, ptrdiff_t end)
 
   bset_redisplay (buf);
 
-  ++BUF_OVERLAY_MODIFF (buf);
+  modiff_incr (&BUF_OVERLAY_MODIFF (buf));
 }
 
 /* Remove OVERLAY from LIST.  */