anchor.diff:             (setq tmp-real-nsec-before-gc (papi-get-real-nsec))
              (setq tmp-user-nsec-before-gc (papi-get-virt-nsec)))
             (:after
  -           (papi-accum handle gc-values)
  +           (unless empty-papi-set-p
  +             (papi-accum handle gc-values))
              (incf real-nsec-gc
                    (- (papi-get-real-nsec) tmp-real-nsec-before-gc))
              (incf user-nsec-gc
  
positive.code:              (incf vcsw-gc (- vcsw tmp-vcsw-before-gc))
               (incf ivcsw-gc (- ivcsw tmp-ivcsw-before-gc))))
          (locally (declare (optimize (speed 3) (safety 0)))
            (papi-start handle)
            (setq user-nsec-total (papi-get-virt-nsec))
            (setq real-nsec-total (papi-get-real-nsec))
            (setq return-values (multiple-value-list (funcall function)))
            (setq real-nsec-total (- (papi-get-real-nsec) real-nsec-total))
            (setq user-nsec-total (- (papi-get-virt-nsec) user-nsec-total))
            (papi-accum handle mutator-values)))
        (papi-stop handle (null-pointer))
        (multiple-value-bind (stime reclaims faults vcsw ivcsw)
            (get-resource-usage)
          (setq system-usec-total (- stime system-usec-total))
  
negative.code:         (setq page-faults-total (- faults page-faults-total))
          (setq vcsw-total (- vcsw vcsw-total))
          (setq ivcsw-total (- ivcsw ivcsw-total)))
        (unless empty-papi-set-p
          (papi-stop handle (null-pointer)))
        ;; Aggregate measurements.
        (let ((hw-event-results
               (loop for event in (events-of event-set) and i from 0 collect
  