diff -r 89e1ee0c796c -r 3b1db2134a9e src/zoom.hpp
--- a/src/zoom.hpp	Sun Nov 18 08:03:48 2007 +0000
+++ b/src/zoom.hpp	Sun Nov 18 13:13:59 2007 +0000
@@ -32,6 +32,13 @@
 
 extern ZoomLevel _saved_scrollpos_zoom;
 
+/**
+ * Scale by zoom level, usually shift left (when zoom > ZOOM_LVL_NORMAL)
+ * When shifting right, value is rounded up
+ * @param value value to shift
+ * @param zoom  zoom level to shift to
+ * @return shifted value
+ */
 static inline int ScaleByZoom(int value, ZoomLevel zoom)
 {
 	if (zoom == ZOOM_LVL_NORMAL) return value;
@@ -39,6 +46,13 @@
 	return (zoom > ZOOM_LVL_NORMAL) ? value << izoom : (value + (1 << -izoom) - 1) >> -izoom;
 }
 
+/**
+ * Scale by zoom level, usually shift right (when zoom > ZOOM_LVL_NORMAL)
+ * When shifting right, value is rounded up
+ * @param value value to shift
+ * @param zoom  zoom level to shift to
+ * @return shifted value
+ */
 static inline int UnScaleByZoom(int value, ZoomLevel zoom)
 {
 	if (zoom == ZOOM_LVL_NORMAL) return value;
@@ -46,4 +60,30 @@
 	return (zoom > ZOOM_LVL_NORMAL) ? (value + (1 << izoom) - 1) >> izoom : value << -izoom;
 }
 
+/**
+ * Scale by zoom level, usually shift left (when zoom > ZOOM_LVL_NORMAL)
+ * @param value value to shift
+ * @param zoom  zoom level to shift to
+ * @return shifted value
+ */
+static inline int ScaleByZoomLower(int value, ZoomLevel zoom)
+{
+	if (zoom == ZOOM_LVL_NORMAL) return value;
+	int izoom = (int)zoom - (int)ZOOM_LVL_NORMAL;
+	return (zoom > ZOOM_LVL_NORMAL) ? value << izoom : value >> -izoom;
+}
+
+/**
+ * Scale by zoom level, usually shift right (when zoom > ZOOM_LVL_NORMAL)
+ * @param value value to shift
+ * @param zoom  zoom level to shift to
+ * @return shifted value
+ */
+static inline int UnScaleByZoomLower(int value, ZoomLevel zoom)
+{
+	if (zoom == ZOOM_LVL_NORMAL) return value;
+	int izoom = (int)zoom - (int)ZOOM_LVL_NORMAL;
+	return (zoom > ZOOM_LVL_NORMAL) ? value >> izoom : value << -izoom;
+}
+
 #endif /* ZOOM_HPP */