(defmacro time-this (cnt &rest body)
  (let ((real-t (gensym)) (run-t (gensym)))
    `(let (,real-t ,run-t)
       (setf ,real-t (get-internal-real-time)
	     ,run-t  (get-internal-run-time))
       (loop repeat ,cnt do ,@body)
       (list (/ (- (get-internal-real-time) ,real-t)
		(coerce internal-time-units-per-second 'float))
	     (/ (- (get-internal-run-time) ,run-t)
		(coerce internal-time-units-per-second 'float))))))