Re: Vector and List Performance

[pjb@informatimago.com (Pascal J. Bourguignon)]

Nordlöw <per.nordlow@gmail.com> writes:

> On Jun 9, 2:51 pm, p...@informatimago.com (Pascal J. Bourguignon)
> wrote:
>> Nordlöw <per.nord...@gmail.com> writes:
>> > Aahh, we needed a macro instead:
>>
>> > (defmacro bench (&rest forms)
>> >     "Convenience wrapper for benchmark-run-compiled."
>> >     `(let ((n 10))
>> >        (/ (nth 0 (benchmark-run n ,@forms)) n)))
>>
>> > This gives a reasonable difference in performance.
>>
>> > By the way, does elisp lists have extra pointers to the middle of the
>> > list (a skip-list)?
>>
>> No, because it wouldn't be efficient to have to maintain them.
>>
>> (let* ((c (list 7 8 9))
>>        (b (list* 4 5 6 c))
>>        (a (list* 1 2 3 b)))
>>     (push -1 (cddr c))  (push -2 (cddr c))  ; you may have to update a big number of skip-lists!
>>     (list a b c))
>> -->
>> ((1 2 3 . #1=(4 5 6 . #2=(7 8 -2 -1 9))) #1# #2#)
>>
>> (deftype list () '(or null (cons t list))) ; nothing more.
>>
>> --
>> __Pascal Bourguignon__
>
> I tested the performance difference and strangely the vector version
> of my benchmarking is only faster when the number of elements exceeds
> roughy 1000. Why is this? Shouldn' aref() always be faster than nth
> regardless of the size of the sequence?

How could we say?  You don't provide the full source of what you tested.

Check my other post in this thread, and see how faster the vector
accesses are.  Try the same form in your CL implementation, and report
the results here.

-- 
__Pascal Bourguignon__