anchor.diff:            stop-event (cffi:foreign-alloc 'cu-event))
       (cu-event-create start-event cu-event-default)
       (cu-event-create stop-event cu-event-default))
  -
  +  
     (defun destroy-timer-events ()
       (cu-event-destroy (cffi:mem-ref start-event 'cu-event))
       (cu-event-destroy (cffi:mem-ref stop-event 'cu-event))
  
positive.code:     (incf fps-count)
      (when (>= fps-count fps-limit)
        (multiple-value-bind (ifps interactions-per-second gflops)
                             (compute-perf-stats num-bodies (get-elapsed-time) fps-count 1)
          (glut:set-window-title
            (format nil template num-bodies ifps interactions-per-second gflops))
          (setf fps-count 0)
  
negative.code:     (let* ((ifps (/ 1.0 (/ milliseconds 1000.0)))
             (interactions-per-second (/ (* num-bodies num-bodies iterations)
                                         (/ milliseconds 1000)
                                         1.0e9))
             (gflops (* interactions-per-second *flops-per-interaction*)))
        (values ifps interactions-per-second gflops))))
  
  (let ((fps-count 0)
  