From 5dc65c10ca1a2504699ad5374fedb127960946c8 Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Mon, 1 Aug 2022 15:52:12 +0000
Subject: [PATCH] Various improvements to long lines handling.

* src/xdisp.c (get_visually_first_element,
(move_it_vertically_backward): Do not go back too far with bidi.
(get_narrowed_begv): Do not return 0 anymore instead of BEGV.
(handle_fontified_prop): Simplify accordingly.

* src/keyboard.c (safe_run_hooks_maybe_narrowed): Simplify accordingly.

* src/composite.c (find_automatic_composition): Ditto.
---
 src/composite.c |  2 +-
 src/keyboard.c  |  9 +++------
 src/xdisp.c     | 11 ++++-------
 3 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/src/composite.c b/src/composite.c
index 0f90b92a785..e721fe8c81f 100644
--- a/src/composite.c
+++ b/src/composite.c
@@ -1600,7 +1600,7 @@ find_automatic_composition (ptrdiff_t pos, ptrdiff_t limit, ptrdiff_t backlim,
       /* In buffers with very long lines, this function becomes very
 	 slow.  Pretend that the buffer is narrowed to make it fast.  */
       narrowed_begv = get_narrowed_begv (w, window_point (w));
-      if (narrowed_begv && pos > narrowed_begv)
+      if (pos > narrowed_begv)
 	head = narrowed_begv;
       tail = ZV;
       stop = GPT;
diff --git a/src/keyboard.c b/src/keyboard.c
index 094119340e1..a730dfe4fda 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -1907,12 +1907,9 @@ safe_run_hooks_maybe_narrowed (Lisp_Object hook, struct window *w)
   specbind (Qinhibit_quit, Qt);
 
   if (current_buffer->long_line_optimizations_p)
-    {
-      ptrdiff_t begv = get_narrowed_begv (w, PT);
-      ptrdiff_t zv = get_narrowed_zv (w, PT);
-      if (!begv) begv = BEGV;
-      Fnarrow_to_region (make_fixnum (begv), make_fixnum (zv), Qt);
-    }
+    Fnarrow_to_region (make_fixnum (get_narrowed_begv (w, PT)),
+		       make_fixnum (get_narrowed_zv (w, PT)),
+		       Qt);
 
   run_hook_with_args (2, ((Lisp_Object []) {hook, hook}), safe_run_hook_funcall);
   unbind_to (count, Qnil);
diff --git a/src/xdisp.c b/src/xdisp.c
index c6fc05b8b4a..c4abe6e9855 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -3507,9 +3507,7 @@ ptrdiff_t
 get_narrowed_begv (struct window *w, ptrdiff_t pos)
 {
   int len = get_narrowed_len (w);
-  ptrdiff_t begv;
-  begv = max ((pos / len - 1) * len, BEGV);
-  return begv == BEGV ? 0 : begv;
+  return max ((pos / len - 1) * len, BEGV);
 }
 
 ptrdiff_t
@@ -4394,13 +4392,12 @@ handle_fontified_prop (struct it *it)
 
       if (current_buffer->long_line_optimizations_p)
 	{
-	  ptrdiff_t begv = it->narrowed_begv ? it->narrowed_begv : BEGV;
+	  ptrdiff_t begv = it->narrowed_begv;
 	  ptrdiff_t zv = it->narrowed_zv;
 	  ptrdiff_t charpos = IT_CHARPOS (*it);
 	  if (charpos < begv || charpos > zv)
 	    {
 	      begv = get_narrowed_begv (it->w, charpos);
-	      if (!begv) begv = BEGV;
 	      zv = get_narrowed_zv (it->w, charpos);
 	    }
 	  Fnarrow_to_region (make_fixnum (begv), make_fixnum (zv), Qt);
@@ -8894,7 +8891,7 @@ get_visually_first_element (struct it *it)
 				find_newline_no_quit (IT_CHARPOS (*it),
 						      IT_BYTEPOS (*it), -1,
 						      &it->bidi_it.bytepos),
-				it->narrowed_begv);
+				get_closer_narrowed_begv (it->w, IT_CHARPOS (*it)));
       bidi_paragraph_init (it->paragraph_embedding, &it->bidi_it, true);
       do
 	{
@@ -10784,7 +10781,7 @@ move_it_vertically_backward (struct it *it, int dy)
 	  dec_both (&cp, &bp);
 	  SET_WITH_NARROWED_BEGV (it, cp,
 				  find_newline_no_quit (cp, bp, -1, NULL),
-				  it->narrowed_begv);
+				  get_closer_narrowed_begv (it->w, IT_CHARPOS (*it)));
 	  move_it_to (it, cp, -1, -1, -1, MOVE_TO_POS);
 	}
       bidi_unshelve_cache (it3data, true);
-- 
2.39.2