(define (msecs v)
  (quotient (* v 1000) internal-time-units-per-second))

(define (repeat* n thunk)
  (let loop ((n n))
    (if (= n 0)
        (values)
        (begin
          (thunk)
          (repeat* (- n 1) thunk)))))

(define-syntax repeat
  (syntax-rules ()
    ((_ n expr)
     (repeat* n (lambda () expr)))))

(define (%time thunk)
  (let ((start (times)))
    (let ((v (thunk)))
      (let ((end (times)))
        (msecs (- (tms:utime end) (tms:utime start)))))))

(define (time* n thunk)
  (display
   (- (%time (lambda () (repeat* n thunk)))
      (%time (lambda () (repeat* n (lambda () #f))))))
  (newline))

(define-syntax time
  (syntax-rules ()
    ((_ n expr) (time* n (lambda () expr)))))