Further tweaks to long lines handling.

* src/xdisp.c (redisplay_window): Increase the threshold above which
long lines detection is performed in the buffer.  This should avoid
triggering that detection for most simple editing operations.

* src/lisp.h (modiff_incr): Explain why the counter is incremented
logarithmically.

* src/buffer.h (struct buffer_text): Adapt the comment about the
'modiff' field accordingly.

* src/buffer.c (modify_overlay): Increase the counter by 1 instead of
the size of the buffer section on which the overlay is placed.

* etc/NEWS: Small improvement.

1 files changed, 4 insertions, 3 deletions

diff --git a/src/buffer.h b/src/buffer.h
index 09daa29992a..47b4bdf749b 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -237,9 +237,10 @@ struct buffer_text
     ptrdiff_t z_byte;           /* Byte pos of end of buffer.  */
     ptrdiff_t gap_size;         /* Size of buffer's gap.  */
     modiff_count modiff;        /* This counts buffer-modification events
-                                   for this buffer.  It is incremented for
-                                   each such event, and never otherwise
-                                   changed.  */
+                                   for this buffer.  It is increased
+                                   logarithmically to the extent of the
+                                   modification for each such event,
+                                   and never otherwise changed.  */
     modiff_count chars_modiff;  /* This is modified with character change
                                    events for this buffer.  It is set to
                                    modiff for each such event, and never