real time and run time functions revisited

Hello, here is another attempt at some user-level time functions.
Example session:

(%i1) [absolute_real_time(), ?sleep(5), absolute_real_time()];
(%o1)            [3376334552, false, 3376334557]

(%i2) [elapsed_real_time(), ?sleep(5), elapsed_real_time()];
(%o2)                 [12.91, false, 17.92]

(%i3) [elapsed_run_time(), ?sleep(5), elapsed_run_time()];
(%o3)                  [0.02, false, 0.02]

(%i4) [elapsed_run_time(), factor(expand((a + b)^200)), elapsed_run_time()];
(%o4)               [0.02, (b + a)^200, 1.39]

absolute_real_time returns number of seconds since 1900/01/01
(as specified for the CL function get-universal-time).

Hope this helps,
Robert

PS. Here is the code. initialize-real-and-run-time is called from
cl-user::run (same place as some other initialization functions).

(let
  ((t0-real 0) (t0-run 0)
   (float-units (float internal-time-units-per-second 1d0)))

  (defun initialize-real-and-run-time ()
    (setq t0-real (get-internal-real-time))
    (setq t0-run (get-internal-run-time)))

  (defun $absolute_real_time () (get-universal-time))

  (defun $elapsed_real_time ()
    (let ((elapsed-real-time (- (get-internal-real-time) t0-real)))
      (/ elapsed-real-time float-units)))

  (defun $elapsed_run_time ()
    (let ((elapsed-run-time (- (get-internal-run-time) t0-run)))
      (/ elapsed-run-time float-units))))