Elisp Running Time Macro

I wanted an elisp macro that could measure the running time of a block of code. Specifically, I wanted it to work like this,


And it would return the running time as seconds in floating point. Well, here's a macro that does it!

;; ID: 6a3f3d99-f0da-329a-c01c-bb6b868f3239
(defmacro measure-time (&rest body)
  "Measure and return the running time of the code block."
  (declare (indent defun))
  (let ((start (make-symbol "start")))
    `(let ((,start (float-time)))
       (- (float-time) ,start))))

It's only good for up to around 18 hours, then the time integer overflows. If only Emacs had arbitrary precision numbers. Here it is in action using my binomial function from last week.

  (nck 20 10)
  (nck 30 7))

Which, just now, returned 3.643713 seconds when executed.

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Chris Wellons

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