ui/vnc: optimize setting in vnc_dpy_update()

Signed-off-by: NPeter Lieven <pl@kamp.de>
Reviewed-by: NWenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/vnc.c

@@ -430,30 +430,24 @@ static int vnc_refresh_server_surface(VncDisplay *vd);
 static void vnc_dpy_update(DisplayChangeListener *dcl,
                            int x, int y, int w, int h)
 {
-    int i;
     VncDisplay *vd = container_of(dcl, VncDisplay, dcl);
     struct VncSurface *s = &vd->guest;
     int width = surface_width(vd->ds);
     int height = surface_height(vd->ds);
 
-    h += y;
-
-    /* round x down to ensure the loop only spans one 16-pixel block per,
-       iteration.  otherwise, if (x % 16) != 0, the last iteration may span
-       two 16-pixel blocks but we only mark the first as dirty
-    */
+    /* this is needed this to ensure we updated all affected
+     * blocks if x % VNC_DIRTY_PIXELS_PER_BIT != 0 */
     w += (x % VNC_DIRTY_PIXELS_PER_BIT);
     x -= (x % VNC_DIRTY_PIXELS_PER_BIT);
 
     x = MIN(x, width);
     y = MIN(y, height);
     w = MIN(x + w, width) - x;
-    h = MIN(h, height);
+    h = MIN(y + h, height);
 
     for (; y < h; y++) {
-        for (i = 0; i < w; i += VNC_DIRTY_PIXELS_PER_BIT) {
-            set_bit((x + i) / VNC_DIRTY_PIXELS_PER_BIT, s->dirty[y]);
-        }
+        bitmap_set(s->dirty[y], x / VNC_DIRTY_PIXELS_PER_BIT,
+                   DIV_ROUND_UP(w, VNC_DIRTY_PIXELS_PER_BIT));
     }
 }