Improvements to long lines handling.

* src/buffer.h (struct buffer): New field 'long_line_optimizations_p'.

* src/buffer.c (syms_of_buffer): New variable 'long-line-threshold'.
(reset_buffer): Initialize the 'long_line_optimizations_p' field.
(Fbuffer_swap_text): Handle it.

* src/xdisp.c (redisplay_window): Set 'long_line_optimizations_p' when
a buffer contains long lines.
(init_iterator): Use 'long_line_optimizations_p'.
(get_narrowed_begv): Update.
(SET_WITH_NARROWED_BEGV): New macro.
(unwind_narrowed_begv): New internal function used by the new macro.
(back_to_previous_line_start, get_visually_first_element,
move_it_vertically_backward): Use the new macro.

* src/search.c (find_newline1): Make it externally visible.

* src/lisp.h: Make 'find_newline1' externally visible.

* src/dispextern.h (struct it): Update comment.  Remove the
'WITH_NARROWED_BEGV' macro.

* etc/NEWS: Mention the 'long-line-threshold' variable.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 509ce51b55e..a777668e44b 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -984,6 +984,7 @@ reset_buffer (register struct buffer *b)
   /* It is more conservative to start out "changed" than "unchanged".  */
   b->clip_changed = 0;
   b->prevent_redisplay_optimizations_p = 1;
+  b->long_line_optimizations_p = 0;
   bset_backed_up (b, Qnil);
   bset_local_minor_modes (b, Qnil);
   BUF_AUTOSAVE_MODIFF (b) = 0;
@@ -2445,6 +2446,7 @@ results, see Info node `(elisp)Swapping Text'.  */)
   swapfield (bidi_paragraph_cache, struct region_cache *);
   current_buffer->prevent_redisplay_optimizations_p = 1;
   other_buffer->prevent_redisplay_optimizations_p = 1;
+  swapfield (long_line_optimizations_p, bool_bf);
   swapfield (overlays_before, struct Lisp_Overlay *);
   swapfield (overlays_after, struct Lisp_Overlay *);
   swapfield (overlay_center, ptrdiff_t);
@@ -6423,6 +6425,14 @@ Since `clone-indirect-buffer' calls `make-indirect-buffer', this hook
 will run for `clone-indirect-buffer' calls as well.  */);
   Vclone_indirect_buffer_hook = Qnil;
 
+  DEFVAR_LISP ("long-line-threshold", Vlong_line_threshold,
+               doc: /* Line length above which specific display optimizations are used.
+Display optimizations for long lines will automatically be enabled in
+buffers which contain one or more lines whose length is above that
+threshold.
+When nil, these display optimizations are disabled.  */);
+  XSETFASTINT (Vlong_line_threshold, 10000);
+
   defsubr (&Sbuffer_live_p);
   defsubr (&Sbuffer_list);
   defsubr (&Sget_buffer);