Speed up cursor motion in large fontified buffers.

 src/xdisp.c (reseat): Don't look for prev_stop, as that could mean a
 very long run.
 (next_element_from_buffer): When iterator oversteps prev_pos
 backwards, don't search for a new prev_stop more than 1000
 characters back.
 (handle_stop_backwards): Don't assume that CHARPOS is necessarily
 a stop_pos.
 (compute_display_string_pos): Check also BUF_OVERLAY_MODIFF for a
 match, when testing the cached display string position for
 applicability.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 0114495838f..15f37f486e2 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,18 @@
+2011-07-19  Eli Zaretskii  <eliz@gnu.org>
+
+        Fix a significant slow-down of vertical-motion when leaning on C-n
+        or C-p in a fontified buffer.
+        * xdisp.c (reseat): Don't look for prev_stop, as that could mean a
+        very long run.
+        (next_element_from_buffer): When iterator oversteps prev_pos
+        backwards, don't search for a new prev_stop more than 1000
+        characters back.
+        (handle_stop_backwards): Don't assume that CHARPOS is necessarily
+        a stop_pos.
+        (compute_display_string_pos): Check also BUF_OVERLAY_MODIFF for a
+        match, when testing the cached display string position for
+        applicability.
+
 2011-07-16  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c <cached_disp_pos, cached_disp_buffer, cached_disp_modiff>: