+ /*
+ * First run of @dst that needs to be moved out of the way to make
+ * space for the runs to be copied from @src, i.e. the first run of the
+ * tail of @dst.
+ */
+ tail = loc + right + 1;
+ /*
+ * First run after the @src runs that have been inserted, i.e. where
+ * the tail of @dst needs to be moved to.
+ * Nominally, marker equals @loc + @ssize, i.e. location + number of
+ * runs in @src). However, if @left, then the first run in @src has
+ * been merged with one in @dst.
+ */
+ marker = loc + ssize - left;