Fix scrolling back with scroll-down-aggressively.

 src/xdisp.c (try_scrolling): Clean up the case of PT below the
 margin at bottom of window: scroll_max can no longer be INT_MAX.
 (redisplay_window): Find character position of margin and use
 that, rather than adding margin to PT.

2 files changed, 28 insertions, 9 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index d4301c482e9..e7a93ab7819 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,10 @@
+2011-03-27  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (try_scrolling): Clean up the case of PT below the
+        margin at bottom of window: scroll_max can no longer be INT_MAX.
+        (redisplay_window): Find character position of margin and use
+        that, rather than adding margin to PT.
+
 2011-03-26  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (redisplay_window): Don't check buffer's clip_changed
diff --git a/src/xdisp.c b/src/xdisp.c
index 230e2fa1864..1b72f2e3081 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -13083,10 +13083,7 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
              always finds PT if scroll_conservatively is set to a large
              number, such as most-positive-fixnum.  */
           int slack = max (scroll_max, 10 * FRAME_LINE_HEIGHT (f));
-          int y_to_move =
-            slack >= INT_MAX - it.last_visible_y
-            ? INT_MAX
-            : it.last_visible_y + slack;
+          int y_to_move = it.last_visible_y + slack;
 
           /* Compute the distance from the scroll margin to PT or to
              the scroll limit, whichever comes first.  This should
@@ -13198,8 +13195,8 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
           start_display (&it, w, startp);
 
           if (arg_scroll_conservatively)
-            amount_to_scroll
-              = max (dy, FRAME_LINE_HEIGHT (f) * max (scroll_step, temp_scroll_step));
+            amount_to_scroll = max (dy, FRAME_LINE_HEIGHT (f) *
+                                    max (scroll_step, temp_scroll_step));
           else if (scroll_step || temp_scroll_step)
             amount_to_scroll = scroll_max;
           else
@@ -14238,8 +14235,22 @@ redisplay_window (Lisp_Object window, int just_this_one_p)
         scroll_margin > 0
         ? min (scroll_margin, WINDOW_TOTAL_LINES (w) / 4)
         : 0;
-      int scrolling_up = PT > CHARPOS (startp) + margin;
-      Lisp_Object aggressive =
+      EMACS_INT margin_pos = CHARPOS (startp);
+      int scrolling_up;
+      Lisp_Object aggressive;
+
+      /* If there is a scroll margin at the top of the window, find
+         its character position.  */
+      if (margin)
+        {
+          struct it it1;
+
+          start_display (&it1, w, startp);
+          move_it_vertically (&it1, margin);
+          margin_pos = IT_CHARPOS (it1);
+        }
+      scrolling_up = PT > margin_pos;
+      aggressive =
         scrolling_up
         ? BVAR (current_buffer, scroll_up_aggressively)
         : BVAR (current_buffer, scroll_down_aggressively);
@@ -14280,7 +14291,8 @@ redisplay_window (Lisp_Object window, int just_this_one_p)
             centering_position = margin * FRAME_LINE_HEIGHT (f) + pt_offset;
         }
       else
-        /* Move backward from point half the height of the window.  */
+        /* Set the window start half the height of the window backward
+           from point.  */
         centering_position = window_box_height (w) / 2;
     }
   move_it_vertically_backward (&it, centering_position);