Use region cache to speedup bidi_find_paragraph_start.

* src/buffer.h (struct buffer): New member bidi_paragraph_cache.
Rename cache_long_line_scans to cache_long_scans.
* src/buffer.c (bset_cache_long_line_scans): Rename to
bset_cache_long_scans.
(Fget_buffer_create, Fmake_indirect_buffer, Fkill_buffer)
(Fbuffer_swap_text, init_buffer_once): Take bidi_paragraph_cache
into account.
(syms_of_buffer): Rename cache-long-line-scans to
cache-long-scans.  Adjust docstring.
* src/search.c (newline_cache_on_off):
* src/indent.c (width_run_cache_on_off): Adjust users.
* src/bidi.c (bidi_paragraph_cache_on_off): New function.
(bidi_find_paragraph_start): Use bidi_paragraph_cache if needed.
* src/insdel.c (prepare_to_modify_buffer): Invalidate
bidi_paragraph_cache if enabled.
* doc/lispref/positions.texi (Motion by Screen Lines):
* doc/lispref/display.texi (Truncation): Rename `cache-long-line-scans'
to `cache-long-scans'.

1 files changed, 22 insertions, 8 deletions

diff --git a/src/buffer.c b/src/buffer.c
index f9154d42b03..339175d9078 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -203,9 +203,9 @@ bset_buffer_file_coding_system (struct buffer *b, Lisp_Object val)
   b->INTERNAL_FIELD (buffer_file_coding_system) = val;
 }
 static void
-bset_cache_long_line_scans (struct buffer *b, Lisp_Object val)
+bset_cache_long_scans (struct buffer *b, Lisp_Object val)
 {
-  b->INTERNAL_FIELD (cache_long_line_scans) = val;
+  b->INTERNAL_FIELD (cache_long_scans) = val;
 }
 static void
 bset_case_fold_search (struct buffer *b, Lisp_Object val)
@@ -583,6 +583,7 @@ even if it is dead.  The return value is never nil.  */)
 
   b->newline_cache = 0;
   b->width_run_cache = 0;
+  b->bidi_paragraph_cache = 0;
   bset_width_table (b, Qnil);
   b->prevent_redisplay_optimizations_p = 1;
 
@@ -806,6 +807,7 @@ CLONE nil means the indirect buffer's state is reset to default values.  */)
 
   b->newline_cache = 0;
   b->width_run_cache = 0;
+  b->bidi_paragraph_cache = 0;
   bset_width_table (b, Qnil);
 
   name = Fcopy_sequence (name);
@@ -1945,6 +1947,11 @@ cleaning up all windows currently displaying the buffer to be killed. */)
       free_region_cache (b->width_run_cache);
       b->width_run_cache = 0;
     }
+  if (b->bidi_paragraph_cache)
+    {
+      free_region_cache (b->bidi_paragraph_cache);
+      b->bidi_paragraph_cache = 0;
+    }
   bset_width_table (b, Qnil);
   unblock_input ();
   bset_undo_list (b, Qnil);
@@ -2355,6 +2362,7 @@ DEFUN ("buffer-swap-text", Fbuffer_swap_text, Sbuffer_swap_text,
   current_buffer->clip_changed = 1;     other_buffer->clip_changed = 1;
   swapfield (newline_cache, struct region_cache *);
   swapfield (width_run_cache, struct region_cache *);
+  swapfield (bidi_paragraph_cache, struct region_cache *);
   current_buffer->prevent_redisplay_optimizations_p = 1;
   other_buffer->prevent_redisplay_optimizations_p = 1;
   swapfield (overlays_before, struct Lisp_Overlay *);
@@ -5169,7 +5177,7 @@ init_buffer_once (void)
   bset_buffer_file_coding_system (&buffer_defaults, Qnil);
   XSETFASTINT (BVAR (&buffer_defaults, fill_column), 70);
   XSETFASTINT (BVAR (&buffer_defaults, left_margin), 0);
-  bset_cache_long_line_scans (&buffer_defaults, Qnil);
+  bset_cache_long_scans (&buffer_defaults, Qnil);
   bset_file_truename (&buffer_defaults, Qnil);
   XSETFASTINT (BVAR (&buffer_defaults, display_count), 0);
   XSETFASTINT (BVAR (&buffer_defaults, left_margin_cols), 0);
@@ -5233,7 +5241,7 @@ init_buffer_once (void)
   XSETFASTINT (BVAR (&buffer_local_flags, abbrev_table), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, display_table), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, syntax_table), idx); ++idx;
-  XSETFASTINT (BVAR (&buffer_local_flags, cache_long_line_scans), idx); ++idx;
+  XSETFASTINT (BVAR (&buffer_local_flags, cache_long_scans), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, category_table), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, bidi_display_reordering), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, bidi_paragraph_direction), idx); ++idx;
@@ -6120,8 +6128,8 @@ If the value of the variable is t, undo information is not recorded.  */);
   DEFVAR_PER_BUFFER ("mark-active", &BVAR (current_buffer, mark_active), Qnil,
                      doc: /* Non-nil means the mark and region are currently active in this buffer.  */);
 
-  DEFVAR_PER_BUFFER ("cache-long-line-scans", &BVAR (current_buffer, cache_long_line_scans), Qnil,
-                     doc: /* Non-nil means that Emacs should use caches to handle long lines more quickly.
+  DEFVAR_PER_BUFFER ("cache-long-scans", &BVAR (current_buffer, cache_long_scans), Qnil,
+                     doc: /* Non-nil means that Emacs should use caches in attempt to speedup buffer scans.
 
 Normally, the line-motion functions work by scanning the buffer for
 newlines.  Columnar operations (like `move-to-column' and
@@ -6131,18 +6139,24 @@ buffer's lines are very long (say, more than 500 characters), these
 motion functions will take longer to execute.  Emacs may also take
 longer to update the display.
 
-If `cache-long-line-scans' is non-nil, these motion functions cache the
+If `cache-long-scans' is non-nil, these motion functions cache the
 results of their scans, and consult the cache to avoid rescanning
 regions of the buffer until the text is modified.  The caches are most
 beneficial when they prevent the most searching---that is, when the
 buffer contains long lines and large regions of characters with the
 same, fixed screen width.
 
-When `cache-long-line-scans' is non-nil, processing short lines will
+When `cache-long-scans' is non-nil, processing short lines will
 become slightly slower (because of the overhead of consulting the
 cache), and the caches will use memory roughly proportional to the
 number of newlines and characters whose screen width varies.
 
+Bidirectional editing also requires buffer scans to find paragraph
+separators.  If you have large paragraphs or no paragraph separators
+at all, these scans may be slow.  If `cache-long-scans' is non-nil,
+results of these scans are cached.  This doesn't help too much if
+paragraphs are of the reasonable (few thousands of characters) size.
+
 The caches require no explicit maintenance; their accuracy is
 maintained internally by the Emacs primitives.  Enabling or disabling
 the cache should not affect the behavior of any of the motion