UDB_REL_PTR
UDB_REL_PTR(rp->next)->prev = r;
UDB_REL_PTR(rp->prev)->next = r;
p = UDB_REL_PTR(p)->next;
UDB_REL_PTR(ptr->prev)->next = ptr->next;
UDB_REL_PTR(ptr->next)->prev = ptr->prev;
UDB_REL_PTR(ptr->next)->prev = UDB_SYSTOREL(base, ptr);
UDB_REL_PTR(p)->data = to;
p = UDB_REL_PTR(p)->next;