(Frecenter): Simplify computation in the case of window

system frames and ARG < 0; use window_box_height.

1 files changed, 4 insertions, 5 deletions

diff --git a/src/window.c b/src/window.c
index 7d0a1eec6cd..6ee3086d616 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4584,18 +4584,17 @@ and redisplay normally--don't erase and redraw the frame.  */)
           nlines = - XINT (arg) - 1;
           move_it_by_lines (&it, nlines, 1);
 
-          y1 = it.current_y - y0;
-          h = line_bottom_y (&it) - y1;
+          y1 = line_bottom_y (&it);
 
           /* If we can't move down NLINES lines because we hit
              the end of the buffer, count in some empty lines.  */
           if (it.vpos < nlines)
             y1 += (nlines - it.vpos) * CANON_Y_UNIT (it.f);
           
-          y0 = it.last_visible_y - y1 - h;
-          
+          h = window_box_height (w) - (y1 - y0);
+
           start_display (&it, w, pt);
-          move_it_vertically (&it, - y0);
+          move_it_vertically (&it, - h);
           charpos = IT_CHARPOS (it);
           bytepos = IT_BYTEPOS (it);
         }