vim-patch:9.1.0215: Half-page scrolling does not support smooth-scrolling

Problem:  Page-wise scrolling with Ctrl-D/Ctrl-U implements
          it's own logic to change the topline and cursor.
          More logic than necessary for scrolling with Ctrl-F/Ctrl-B
          was removed in patch 9.1.0211.
Solution: Re-use the logic from Ctrl-E/Ctrl-Y/Ctrl-F/Ctrl-B while
          staying backward compatible as much as possible.
          Restore some of the logic that determined how many lines will
          be scrolled (Luuk van Baal)

https://github.com/vim/vim/commit/5a2e3ec9ac72b6e644fea4ebba7e632498296e2f

11 files changed, 159 insertions, 178 deletions

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 043524e976..b0583d306d 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -5694,7 +5694,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	You may also want to add "lastline" to the 'display' option to show as
 	much of the last line as possible.
 	NOTE: only partly implemented, currently works with CTRL-E, CTRL-Y,
-	CTRL-B, CTRL-F and scrolling with the mouse.
+	CTRL-D, CTRL-U, CTRL-F, CTRL-B and scrolling with the mouse.
 
 						*'softtabstop'* *'sts'*
 'softtabstop' 'sts'	number	(default 0)
@@ -7164,8 +7164,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 	will scroll 'window' minus two lines, with a minimum of one.
 	When 'window' is equal to 'lines' minus one CTRL-F and CTRL-B scroll
 	in a much smarter way, taking care of wrapping lines.
-	When resizing the Vim window, the value is smaller than 1 or more than
-	or equal to 'lines' it will be set to 'lines' minus 1.
+	When resizing the Vim window, and the value is smaller than 1 or more
+	than or equal to 'lines' it will be set to 'lines' minus 1.
 	Note: Do not confuse this with the height of the Vim window, use
 	'lines' for that.
 
diff --git a/runtime/lua/vim/_meta/options.lua b/runtime/lua/vim/_meta/options.lua
index 2d78013208..adc42f9659 100644
--- a/runtime/lua/vim/_meta/options.lua
+++ b/runtime/lua/vim/_meta/options.lua
@@ -6076,7 +6076,7 @@ vim.go.sta = vim.go.smarttab
 --- You may also want to add "lastline" to the 'display' option to show as
 --- much of the last line as possible.
 --- NOTE: only partly implemented, currently works with CTRL-E, CTRL-Y,
---- CTRL-B, CTRL-F and scrolling with the mouse.
+--- CTRL-D, CTRL-U, CTRL-F, CTRL-B and scrolling with the mouse.
 ---
 --- @type boolean
 vim.o.smoothscroll = false
@@ -7861,8 +7861,8 @@ vim.wo.winbl = vim.wo.winblend
 --- will scroll 'window' minus two lines, with a minimum of one.
 --- When 'window' is equal to 'lines' minus one CTRL-F and CTRL-B scroll
 --- in a much smarter way, taking care of wrapping lines.
---- When resizing the Vim window, the value is smaller than 1 or more than
---- or equal to 'lines' it will be set to 'lines' minus 1.
+--- When resizing the Vim window, and the value is smaller than 1 or more
+--- than or equal to 'lines' it will be set to 'lines' minus 1.
 --- Note: Do not confuse this with the height of the Vim window, use
 --- 'lines' for that.
 ---
diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 5ae5267364..11c5ba2628 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -4193,7 +4193,7 @@ static void ins_pageup(void)
   }
 
   pos_T tpos = curwin->w_cursor;
-  if (onepage(BACKWARD, 1) == OK) {
+  if (pagescroll(BACKWARD, 1, false) == OK) {
     start_arrow(&tpos);
     can_cindent = true;
   } else {
@@ -4238,7 +4238,7 @@ static void ins_pagedown(void)
   }
 
   pos_T tpos = curwin->w_cursor;
-  if (onepage(FORWARD, 1) == OK) {
+  if (pagescroll(FORWARD, 1, false) == OK) {
     start_arrow(&tpos);
     can_cindent = true;
   } else {
diff --git a/src/nvim/mouse.c b/src/nvim/mouse.c
index a2b4042f30..1e70462700 100644
--- a/src/nvim/mouse.c
+++ b/src/nvim/mouse.c
@@ -1024,7 +1024,7 @@ void do_mousescroll(cmdarg_T *cap)
     // Vertical scrolling
     if ((State & MODE_NORMAL) && shift_or_ctrl) {
       // whole page up or down
-      onepage(cap->arg ? FORWARD : BACKWARD, 1);
+      pagescroll(cap->arg ? FORWARD : BACKWARD, 1, false);
     } else {
       if (shift_or_ctrl) {
         // whole page up or down
diff --git a/src/nvim/move.c b/src/nvim/move.c
index ebb27337f7..52b65c0fef 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -2278,19 +2278,90 @@ void cursor_correct(win_T *wp)
   wp->w_viewport_invalid = true;
 }
 
+/// Decide how much overlap to use for page-up or page-down scrolling.
+/// This is symmetric, so that doing both keeps the same lines displayed.
+/// Three lines are examined:
+///
+///  before CTRL-F          after CTRL-F / before CTRL-B
+///     etc.                    l1
+///  l1 last but one line       ------------
+///  l2 last text line          l2 top text line
+///  -------------              l3 second text line
+///  l3                            etc.
+static int get_scroll_overlap(Direction dir)
+{
+  lineoff_T loff;
+  int min_height = curwin->w_height_inner - 2;
+
+  validate_botline(curwin);
+  if (dir == FORWARD && curwin->w_botline > curbuf->b_ml.ml_line_count) {
+    return min_height + 2;  // no overlap, still handle 'smoothscroll'
+  }
+
+  loff.lnum = dir == FORWARD ? curwin->w_botline : curwin->w_topline - 1;
+  loff.fill = win_get_fill(curwin, loff.lnum + dir == BACKWARD)
+              - (dir == FORWARD ? curwin->w_filler_rows : curwin->w_topfill);
+  loff.height = loff.fill > 0 ? 1 : plines_win_nofill(curwin, loff.lnum, true);
+
+  int h1 = loff.height;
+  if (h1 > min_height) {
+    return min_height + 2;  // no overlap
+  }
+  if (dir == FORWARD) {
+    topline_back(curwin, &loff);
+  } else {
+    botline_forw(curwin, &loff);
+  }
+
+  int h2 = loff.height;
+  if (h2 == MAXCOL || h2 + h1 > min_height) {
+    return min_height + 2;  // no overlap
+  }
+  if (dir == FORWARD) {
+    topline_back(curwin, &loff);
+  } else {
+    botline_forw(curwin, &loff);
+  }
+
+  int h3 = loff.height;
+  if (h3 == MAXCOL || h3 + h2 > min_height) {
+    return min_height + 2;  // no overlap
+  }
+  if (dir == FORWARD) {
+    topline_back(curwin, &loff);
+  } else {
+    botline_forw(curwin, &loff);
+  }
+
+  int h4 = loff.height;
+  if (h4 == MAXCOL || h4 + h3 + h2 > min_height || h3 + h2 + h1 > min_height) {
+    return min_height + 1;  // 1 line overlap
+  } else {
+    return min_height;      // 2 lines overlap
+  }
+}
+
 /// Move screen "count" pages up ("dir" is BACKWARD) or down ("dir" is FORWARD)
 /// and update the screen.
 ///
 /// @return  FAIL for failure, OK otherwise.
-int onepage(Direction dir, int count)
+int pagescroll(Direction dir, int count, bool half)
 {
   int prev_topfill = curwin->w_topfill;
   linenr_T prev_topline = curwin->w_topline;
   colnr_T prev_skipcol = curwin->w_skipcol;
 
-  // Scroll 'window' or current window height lines.
-  count *= ((ONE_WINDOW && p_window > 0 && p_window < Rows - 1)
-            ? (int)p_window - 2 : curwin->w_height - 1);
+  if (half) {
+    // Scroll [count], 'scroll' or current window height lines.
+    if (count) {
+      curwin->w_p_scr = MIN(curwin->w_height_inner, count);
+    }
+    count = MIN(curwin->w_height_inner, (int)curwin->w_p_scr);
+  } else {
+    // Scroll 'window' or current window height lines.
+    count *= ((ONE_WINDOW && p_window > 0 && p_window < Rows - 1)
+              ? (int)p_window - 2 : get_scroll_overlap(dir));
+  }
 
   if (curwin->w_p_sms) {
     scroll_redraw(dir == FORWARD, count);
@@ -2307,13 +2378,22 @@ int onepage(Direction dir, int count)
     }
     curwin->w_p_sms = false;
   }
+  // Move cursor to first line of closed fold.
+  foldAdjustCursor(curwin);
 
   int nochange = curwin->w_topline == prev_topline
                  && curwin->w_topfill == prev_topfill
                  && curwin->w_skipcol == prev_skipcol;
 
+  // Error if the viewport did not change and the cursor is already
+  // at the boundary.
   if (nochange) {
-    beep_flush();
+    int prev_cursor = curwin->w_cursor.lnum;
+    curwin->w_cursor.lnum += (count + 1) * (dir == FORWARD ? 1 : -1);
+    check_cursor(curwin);
+    if (curwin->w_cursor.lnum == prev_cursor) {
+      beep_flush();
+    }
   } else if (!curwin->w_p_sms || curwin->w_skipcol == prev_skipcol) {
     beginline(BL_SOL | BL_FIX);
   }
@@ -2321,130 +2401,6 @@ int onepage(Direction dir, int count)
   return nochange;
 }
 
-// Scroll 'scroll' lines up or down.
-void halfpage(bool flag, linenr_T Prenum)
-{
-  int scrolled = 0;
-  int i;
-
-  if (Prenum) {
-    curwin->w_p_scr = (Prenum > curwin->w_height_inner) ? curwin->w_height_inner
-                                                        : Prenum;
-  }
-  assert(curwin->w_p_scr <= INT_MAX);
-  int n = curwin->w_p_scr <= curwin->w_height_inner ? (int)curwin->w_p_scr
-                                                    : curwin->w_height_inner;
-
-  update_topline(curwin);
-  validate_botline(curwin);
-  int room = curwin->w_empty_rows + curwin->w_filler_rows;
-  if (flag) {
-    // scroll the text up
-    while (n > 0 && curwin->w_botline <= curbuf->b_ml.ml_line_count) {
-      if (curwin->w_topfill > 0) {
-        i = 1;
-        n--;
-        curwin->w_topfill--;
-      } else {
-        i = plines_win_nofill(curwin, curwin->w_topline, true);
-        n -= i;
-        if (n < 0 && scrolled > 0) {
-          break;
-        }
-        hasFolding(curwin, curwin->w_topline, NULL, &curwin->w_topline);
-        curwin->w_topline++;
-        curwin->w_topfill = win_get_fill(curwin, curwin->w_topline);
-
-        if (curwin->w_cursor.lnum < curbuf->b_ml.ml_line_count) {
-          curwin->w_cursor.lnum++;
-          curwin->w_valid &=
-            ~(VALID_VIRTCOL|VALID_CHEIGHT|VALID_WCOL);
-        }
-      }
-      curwin->w_valid &= ~(VALID_CROW|VALID_WROW);
-      scrolled += i;
-
-      // Correct w_botline for changed w_topline.
-      // Won't work when there are filler lines.
-      if (win_may_fill(curwin)) {
-        curwin->w_valid &= ~(VALID_BOTLINE|VALID_BOTLINE_AP);
-      } else {
-        room += i;
-        do {
-          i = plines_win(curwin, curwin->w_botline, true);
-          if (i > room) {
-            break;
-          }
-          hasFolding(curwin, curwin->w_botline, NULL, &curwin->w_botline);
-          curwin->w_botline++;
-          room -= i;
-        } while (curwin->w_botline <= curbuf->b_ml.ml_line_count);
-      }
-    }
-
-    // When hit bottom of the file: move cursor down.
-    if (n > 0) {
-      if (hasAnyFolding(curwin)) {
-        while (--n >= 0
-               && curwin->w_cursor.lnum < curbuf->b_ml.ml_line_count) {
-          hasFolding(curwin, curwin->w_cursor.lnum, NULL,
-                     &curwin->w_cursor.lnum);
-          curwin->w_cursor.lnum++;
-        }
-      } else {
-        curwin->w_cursor.lnum += n;
-      }
-      check_cursor_lnum(curwin);
-    }
-  } else {
-    // scroll the text down
-    while (n > 0 && curwin->w_topline > 1) {
-      if (curwin->w_topfill < win_get_fill(curwin, curwin->w_topline)) {
-        i = 1;
-        n--;
-        curwin->w_topfill++;
-      } else {
-        i = plines_win_nofill(curwin, curwin->w_topline - 1, true);
-        n -= i;
-        if (n < 0 && scrolled > 0) {
-          break;
-        }
-        curwin->w_topline--;
-        hasFolding(curwin, curwin->w_topline, &curwin->w_topline, NULL);
-        curwin->w_topfill = 0;
-      }
-      curwin->w_valid &= ~(VALID_CROW|VALID_WROW|
-                           VALID_BOTLINE|VALID_BOTLINE_AP);
-      scrolled += i;
-      if (curwin->w_cursor.lnum > 1) {
-        curwin->w_cursor.lnum--;
-        curwin->w_valid &= ~(VALID_VIRTCOL|VALID_CHEIGHT|VALID_WCOL);
-      }
-    }
-
-    // When hit top of the file: move cursor up.
-    if (n > 0) {
-      if (curwin->w_cursor.lnum <= (linenr_T)n) {
-        curwin->w_cursor.lnum = 1;
-      } else if (hasAnyFolding(curwin)) {
-        while (--n >= 0 && curwin->w_cursor.lnum > 1) {
-          curwin->w_cursor.lnum--;
-          hasFolding(curwin, curwin->w_cursor.lnum,
-                     &curwin->w_cursor.lnum, NULL);
-        }
-      } else {
-        curwin->w_cursor.lnum -= n;
-      }
-    }
-  }
-  // Move cursor to first line of closed fold.
-  foldAdjustCursor(curwin);
-  check_topfill(curwin, !flag);
-  cursor_correct(curwin);
-  beginline(BL_SOL | BL_FIX);
-  redraw_later(curwin, UPD_VALID);
-}
-
 void do_check_cursorbind(void)
 {
   static win_T *prev_curwin = NULL;
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 12f0bb631e..bbba8069c7 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -2258,7 +2258,7 @@ static void nv_page(cmdarg_T *cap)
       goto_tabpage(cap->count0);
     }
   } else {
-    onepage(cap->arg, cap->count1);
+    pagescroll(cap->arg, cap->count1, false);
   }
 }
 
@@ -6394,12 +6394,8 @@ static void nv_at(cmdarg_T *cap)
 /// Handle the CTRL-U and CTRL-D commands.
 static void nv_halfpage(cmdarg_T *cap)
 {
-  if ((cap->cmdchar == Ctrl_U && curwin->w_cursor.lnum == 1)
-      || (cap->cmdchar == Ctrl_D
-          && curwin->w_cursor.lnum == curbuf->b_ml.ml_line_count)) {
-    clearopbeep(cap->oap);
-  } else if (!checkclearop(cap->oap)) {
-    halfpage(cap->cmdchar == Ctrl_D, cap->count0);
+  if (!checkclearop(cap->oap)) {
+    pagescroll(cap->cmdchar == Ctrl_D, cap->count0, true);
   }
 }
 
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index a7c5a97d02..e7acf6f6ef 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -7664,7 +7664,7 @@ return {
         You may also want to add "lastline" to the 'display' option to show as
         much of the last line as possible.
         NOTE: only partly implemented, currently works with CTRL-E, CTRL-Y,
-        CTRL-B, CTRL-F and scrolling with the mouse.
+        CTRL-D, CTRL-U, CTRL-F, CTRL-B and scrolling with the mouse.
       ]=],
       full_name = 'smoothscroll',
       pv_name = 'p_sms',
@@ -9806,8 +9806,8 @@ return {
         will scroll 'window' minus two lines, with a minimum of one.
         When 'window' is equal to 'lines' minus one CTRL-F and CTRL-B scroll
         in a much smarter way, taking care of wrapping lines.
-        When resizing the Vim window, the value is smaller than 1 or more than
-        or equal to 'lines' it will be set to 'lines' minus 1.
+        When resizing the Vim window, and the value is smaller than 1 or more
+        than or equal to 'lines' it will be set to 'lines' minus 1.
         Note: Do not confuse this with the height of the Vim window, use
         'lines' for that.
       ]=],
diff --git a/test/functional/legacy/matchparen_spec.lua b/test/functional/legacy/matchparen_spec.lua
index 7b3f7bd424..adbf15d2e3 100644
--- a/test/functional/legacy/matchparen_spec.lua
+++ b/test/functional/legacy/matchparen_spec.lua
@@ -19,7 +19,7 @@ describe('matchparen', function()
       call cursor(5, 1)
     ]])
 
-    feed('V<c-d><c-d>')
+    feed('V<c-d><c-d>3j')
     screen:expect([[
       {17:{}                             |
       {17:}}                             |
diff --git a/test/old/testdir/test_edit.vim b/test/old/testdir/test_edit.vim
index 2d4314a276..ba084442d1 100644
--- a/test/old/testdir/test_edit.vim
+++ b/test/old/testdir/test_edit.vim
@@ -1312,15 +1312,15 @@ func Test_edit_PAGEUP_PAGEDOWN()
   call feedkeys("i\<PageDown>\<esc>", 'tnix')
   call assert_equal([0, 30, 1, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
-  call assert_equal([0, 30, 1, 0], getpos('.'))
+  call assert_equal([0, 29, 1, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
-  call assert_equal([0, 23, 1, 0], getpos('.'))
+  call assert_equal([0, 21, 1, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
-  call assert_equal([0, 15, 1, 0], getpos('.'))
+  call assert_equal([0, 13, 1, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
   call assert_equal([0, 10, 1, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
-  call assert_equal([0, 10, 11, 0], getpos('.'))
+  call assert_equal([0, 2, 11, 0], getpos('.'))
   " <S-Up> is the same as <PageUp>
   " <S-Down> is the same as <PageDown>
   call cursor(1, 1)
@@ -1335,28 +1335,28 @@ func Test_edit_PAGEUP_PAGEDOWN()
   call feedkeys("i\<S-Down>\<esc>", 'tnix')
   call assert_equal([0, 30, 1, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
-  call assert_equal([0, 30, 1, 0], getpos('.'))
+  call assert_equal([0, 29, 1, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
-  call assert_equal([0, 23, 1, 0], getpos('.'))
+  call assert_equal([0, 21, 1, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
-  call assert_equal([0, 15, 1, 0], getpos('.'))
+  call assert_equal([0, 13, 1, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
   call assert_equal([0, 10, 1, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
-  call assert_equal([0, 10, 11, 0], getpos('.'))
+  call assert_equal([0, 2, 11, 0], getpos('.'))
   set nostartofline
   call cursor(30, 11)
   norm! zt
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
-  call assert_equal([0, 30, 11, 0], getpos('.'))
+  call assert_equal([0, 29, 11, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
-  call assert_equal([0, 23, 11, 0], getpos('.'))
+  call assert_equal([0, 21, 11, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
-  call assert_equal([0, 15, 11, 0], getpos('.'))
+  call assert_equal([0, 13, 11, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
   call assert_equal([0, 10, 11, 0], getpos('.'))
   call feedkeys("A\<PageUp>\<esc>", 'tnix')
-  call assert_equal([0, 10, 11, 0], getpos('.'))
+  call assert_equal([0, 2, 11, 0], getpos('.'))
   call cursor(1, 1)
   call feedkeys("A\<PageDown>\<esc>", 'tnix')
   call assert_equal([0, 9, 11, 0], getpos('.'))
@@ -1373,15 +1373,15 @@ func Test_edit_PAGEUP_PAGEDOWN()
   call cursor(30, 11)
   norm! zt
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
-  call assert_equal([0, 30, 11, 0], getpos('.'))
+  call assert_equal([0, 29, 11, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
-  call assert_equal([0, 23, 11, 0], getpos('.'))
+  call assert_equal([0, 21, 11, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
-  call assert_equal([0, 15, 11, 0], getpos('.'))
+  call assert_equal([0, 13, 11, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
   call assert_equal([0, 10, 11, 0], getpos('.'))
   call feedkeys("A\<S-Up>\<esc>", 'tnix')
-  call assert_equal([0, 10, 11, 0], getpos('.'))
+  call assert_equal([0, 2, 11, 0], getpos('.'))
   call cursor(1, 1)
   call feedkeys("A\<S-Down>\<esc>", 'tnix')
   call assert_equal([0, 9, 11, 0], getpos('.'))
diff --git a/test/old/testdir/test_normal.vim b/test/old/testdir/test_normal.vim
index 644a632413..937f18aa69 100644
--- a/test/old/testdir/test_normal.vim
+++ b/test/old/testdir/test_normal.vim
@@ -1283,9 +1283,13 @@ func Test_vert_scroll_cmds()
   exe "normal \<C-D>"
   call assert_equal(46, line('.'))
   exe "normal \<C-U>"
-  call assert_equal(36, line('.'))
+  call assert_equal(36, line('w0'))
+  call assert_equal(46, line('.'))
   exe "normal \<C-U>"
-  call assert_equal(10, line('.'))
+  call assert_equal(1,  line('w0'))
+  call assert_equal(40, line('.'))
+  exe "normal \<C-U>"
+  call assert_equal(30, line('.'))
   exe "normal \<C-U>"
   call assert_equal(1, line('.'))
   set scroll&
@@ -1306,9 +1310,8 @@ func Test_vert_scroll_cmds()
   call assert_equal(50, line('.'))
   call assert_equal(100, line('w$'))
   normal z.
-  let lnum = winline()
   exe "normal \<C-D>"
-  call assert_equal(lnum, winline())
+  call assert_equal(1, winline())
   call assert_equal(50, line('.'))
   normal zt
   exe "normal \<C-D>"
@@ -3077,7 +3080,8 @@ func Test_normal42_halfpage()
   call assert_equal(2, &scroll)
   set scroll=5
   exe "norm! \<c-u>"
-  call assert_equal('3', getline('.'))
+  call assert_equal('3', getline('w0'))
+  call assert_equal('8', getline('.'))
   1
   set scrolloff=5
   exe "norm! \<c-d>"
@@ -3823,11 +3827,11 @@ func Test_normal_vert_scroll_longline()
   call assert_equal(11, line('.'))
   call assert_equal(1, winline())
   exe "normal \<C-B>"
-  call assert_equal(11, line('.'))
-  call assert_equal(9, winline())
+  call assert_equal(10, line('.'))
+  call assert_equal(10, winline())
   exe "normal \<C-B>\<C-B>"
   call assert_equal(5, line('.'))
-  call assert_equal(1, winline())
+  call assert_equal(5, winline())
 
   bwipe!
 endfunc
@@ -4196,12 +4200,16 @@ func Test_single_line_scroll()
   norm! {
   call assert_equal([0, 1, 1, 0], getpos('.'))
 
-  " Ctrl-B scrolls up with hidden "above" virtual text.
+  " Ctrl-B/Ctrl-U scroll up with hidden "above" virtual text.
   set smoothscroll
   exe "normal \<C-E>"
   call assert_notequal(0, winsaveview().skipcol)
   exe "normal \<C-B>"
   call assert_equal(0, winsaveview().skipcol)
+  exe "normal \<C-E>"
+  call assert_notequal(0, winsaveview().skipcol)
+  exe "normal \<C-U>"
+  call assert_equal(0, winsaveview().skipcol)
 
   set smoothscroll&
   bw!
diff --git a/test/old/testdir/test_scroll_opt.vim b/test/old/testdir/test_scroll_opt.vim
index ebfed77214..fbc714d9cc 100644
--- a/test/old/testdir/test_scroll_opt.vim
+++ b/test/old/testdir/test_scroll_opt.vim
@@ -1008,18 +1008,39 @@ func Test_smoothscroll_page()
   call setline(1, 'abcde '->repeat(150))
 
   exe "norm! \<C-F>"
-  call assert_equal(320, winsaveview().skipcol)
+  call assert_equal(400, winsaveview().skipcol)
   exe "norm! \<C-F>"
-  call assert_equal(640, winsaveview().skipcol)
+  call assert_equal(800, winsaveview().skipcol)
   exe "norm! \<C-F>"
   call assert_equal(880, winsaveview().skipcol)
   exe "norm! \<C-B>"
-  call assert_equal(560, winsaveview().skipcol)
+  call assert_equal(480, winsaveview().skipcol)
   exe "norm! \<C-B>"
-  call assert_equal(240, winsaveview().skipcol)
+  call assert_equal(80, winsaveview().skipcol)
   exe "norm! \<C-B>"
   call assert_equal(0, winsaveview().skipcol)
 
+  exe "norm! \<C-D>"
+  call assert_equal(200, winsaveview().skipcol)
+  exe "norm! \<C-D>"
+  call assert_equal(400, winsaveview().skipcol)
+  exe "norm! \<C-D>"
+  call assert_equal(600, winsaveview().skipcol)
+  exe "norm! \<C-D>"
+  call assert_equal(800, winsaveview().skipcol)
+  exe "norm! \<C-D>"
+  call assert_equal(880, winsaveview().skipcol)
+  exe "norm! \<C-U>"
+  call assert_equal(680, winsaveview().skipcol)
+  exe "norm! \<C-U>"
+  call assert_equal(480, winsaveview().skipcol)
+  exe "norm! \<C-U>"
+  call assert_equal(280, winsaveview().skipcol)
+  exe "norm! \<C-U>"
+  call assert_equal(80, winsaveview().skipcol)
+  exe "norm! \<C-U>"
+  call assert_equal(0, winsaveview().skipcol)
+
   set smoothscroll&
 endfunc