anchor.diff:     (delta-time :initform 0)
      (damping :initform 0)
      (num-bodies :initform 0)
  -   (p :initform 0))
  +   (p :initform 0)
  +   (start-event :initform nil)
  +   (stop-event :initform nil))
     (:default-initargs :width 640 :height 480 :pos-x 100 :pos-y 100
                        :mode '(:double :rgb) :title "nbody"))
   
  
positive.code: (defun update (new-pos old-pos vel delta-time damping num-bodies p)
    (integrate-nbody-system new-pos old-pos vel delta-time damping num-bodies p))
  
  (defun run-benchmark (new-pos old-pos vel delta-time damping num-bodies p iterations)
    (update new-pos old-pos vel delta-time damping num-bodies p)
    ;; create-timer
  
negative.code:         (delta-time 0.016)
          (damping 1.0)
          (p 256))
        (with-cuda-context (dev-id)
          (cffi:with-foreign-objects ((start-event 'cu-event)
                                      (stop-event 'cu-event))
            (cu-event-create start-event cu-event-default)
            (cu-event-create stop-event cu-event-default)
            (with-memory-blocks ((new-pos 'float4 num-bodies)
                                 (old-pos 'float4 num-bodies)
                                 (vel 'float4 num-bodies))
              (reset old-pos vel cluster-scale velocity-scale num-bodies)
              (memcpy-host-to-device old-pos vel)
              (let ((window (make-instance 'nbody-window)))
                (setf (slot-value window 'new-pos) new-pos)
                (setf (slot-value window 'old-pos) old-pos)
                (setf (slot-value window 'vel) vel)
                (setf (slot-value window 'delta-time) delta-time)
                (setf (slot-value window 'damping) damping)
                (setf (slot-value window 'num-bodies) num-bodies)
                (setf (slot-value window 'p) p)
                (setf (slot-value window 'start-event) start-event)
                (setf (slot-value window 'stop-event) stop-event)
                (cu-event-record (cffi:mem-ref start-event 'cu-event)
                                 (cffi:null-pointer))
                (glut:display-window window)))))))
  