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Re: Vector and List Performance
From: |
Tassilo Horn |
Subject: |
Re: Vector and List Performance |
Date: |
Mon, 08 Jun 2009 21:57:29 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.0.94 (gnu/linux) |
Nordlöw <per.nordlow@gmail.com> writes:
Hi!
> (defun bench (&rest forms)
> "Convenience wrapper for benchmark-run-compiled."
> (/ (nth 0 (benchmark-run 1024 forms)) 1024))
>
> (let ((length 1000000))
> (cons
> (bench (aref (make-vector length 0) (/ length 2)))
> (bench (nth (/ length 2) (make-list length 0)))
> ))
>
> Strangely I can't seem to find any significant different in
> performance when accessing the middle element in a long vector and
> long list. Shouldn't the random access performance be the big
> difference between vectors and lists? What have I missed?
I think that there's some optimization under the hood. Actually, you
always access the same place in the list/vector. With real random
access, you get the expected result:
--8<---------------cut here---------------start------------->8---
(defun bench ()
(let* ((len 1000000)
(vec (make-vector len 0))
(lst (make-list len 0))
(times 50000))
(cons
(/ (car (benchmark-run times (aref vec (random len)))) times)
(/ (car (benchmark-run times (nth (random len) lst))) times))))
(bench)
==> (1.5999999999999999e-09 . 1.2723999999999999e-06)
--8<---------------cut here---------------end--------------->8---
So random access on a vector is about 1000 times faster.
Bye,
Tassilo