Comments on: What *warn-on-reflection* doesn’t tell you about arrays http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/ When the pupil is ready to learn, a teacher will appear. Mon, 30 Jan 2012 20:57:36 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Timothy Pratley http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/comment-page-1/#comment-45 Timothy Pratley Mon, 28 Sep 2009 13:00:33 +0000 http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/#comment-45 Ah, thanks! Ah, thanks!

]]> By: cgrand http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/comment-page-1/#comment-44 cgrand Mon, 28 Sep 2009 09:55:32 +0000 http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/#comment-44 @Timothy, I think your tests are dominated by boxed arithmetic. (let [a #^doubles (make-array Double/TYPE 100)] (time (dotimes [i 100000000] (aget a (int (rem i 100)))))) "Elapsed time: 1806.106502 msecs" user=> (let [a (make-array Double/TYPE 100)] (time (dotimes [i 100000000] (aget a (int (rem i 100)))))) "Elapsed time: 17794.809466 msecs" Note that dotimes automatically hints 'i as an int. I measure this difference even for smaller arrays: user=> (let [a #^doubles (make-array Double/TYPE 100)] (time (dotimes [i 100000] (aget a (int (rem i 100)))))) "Elapsed time: 14.871513 msecs" user=> (let [a (make-array Double/TYPE 100)] (time (dotimes [i 100000] (aget a (int (rem i 100)))))) "Elapsed time: 30.586988 msecs" When I hint your code to perform primitive arithmetic, I get similar improvements: user=> (let [a (make-array Double/TYPE 1000000) b #^doubles (make-array Double/TYPE 1000000)] (time (doseq [i (range 1000), j (range 1000)] (aget a (int (+ (int i) (* (int j) 100)))))) (time (doseq [i (range 1000), j (range 1000)] (aget b (int (+ (int i) (* (int j) 100))))))) "Elapsed time: 415.131113 msecs" "Elapsed time: 209.553309 msecs" @Timothy, I think your tests are dominated by boxed arithmetic.
(let [a #^doubles (make-array Double/TYPE 100)]
(time (dotimes [i 100000000] (aget a (int (rem i 100))))))
“Elapsed time: 1806.106502 msecs”
user=> (let [a (make-array Double/TYPE 100)]
(time (dotimes [i 100000000] (aget a (int (rem i 100))))))
“Elapsed time: 17794.809466 msecs”

Note that dotimes automatically hints ‘i as an int.

I measure this difference even for smaller arrays:
user=> (let [a #^doubles (make-array Double/TYPE 100)]
(time (dotimes [i 100000] (aget a (int (rem i 100))))))
“Elapsed time: 14.871513 msecs”
user=> (let [a (make-array Double/TYPE 100)]
(time (dotimes [i 100000] (aget a (int (rem i 100))))))
“Elapsed time: 30.586988 msecs”

When I hint your code to perform primitive arithmetic, I get similar improvements:
user=> (let [a (make-array Double/TYPE 1000000)
b #^doubles (make-array Double/TYPE 1000000)]
(time (doseq [i (range 1000), j (range 1000)] (aget a (int (+ (int i) (* (int j) 100))))))
(time (doseq [i (range 1000), j (range 1000)] (aget b (int (+ (int i) (* (int j) 100)))))))
“Elapsed time: 415.131113 msecs”
“Elapsed time: 209.553309 msecs”

]]> By: Timothy Pratley http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/comment-page-1/#comment-42 Timothy Pratley Sun, 27 Sep 2009 12:58:29 +0000 http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/#comment-42 Hmmm actually I do see a speed-up for larger samples: (let [a (make-array Double/TYPE 1000000) b #^doubles (make-array Double/TYPE 1000000)] (time (doseq [i (range 1000), j (range 1000)] (aget a (int (+ i (* j 100)))))) (time (doseq [i (range 1000), j (range 1000)] (aget b (int (+ i (* j 100))))))) "Elapsed time: 1452.764384 msecs" "Elapsed time: 1118.704557 msecs" Hmmm actually I do see a speed-up for larger samples:

(let [a (make-array Double/TYPE 1000000)
b #^doubles (make-array Double/TYPE 1000000)]
(time (doseq [i (range 1000), j (range 1000)] (aget a (int (+ i (* j 100))))))
(time (doseq [i (range 1000), j (range 1000)] (aget b (int (+ i (* j 100)))))))
“Elapsed time: 1452.764384 msecs”
“Elapsed time: 1118.704557 msecs”

]]> By: Timothy Pratley http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/comment-page-1/#comment-41 Timothy Pratley Sun, 27 Sep 2009 10:59:26 +0000 http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/#comment-41 opps the comment ate the tags, they are ins tags that are leaking through. opps the comment ate the tags,
they are ins tags that are leaking through.

]]> By: Timothy Pratley http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/comment-page-1/#comment-40 Timothy Pratley Sun, 27 Sep 2009 10:58:35 +0000 http://clj-me.cgrand.net/2009/08/06/what-warn-on-reflection-doesnt-tell-you-about-arrays/#comment-40 Very interesting! Sadly this trick doesn't seem to work for arrays of primitives, or my syntax is wrong? (let [a (make-array Double/TYPE 10000) b #^doubles (make-array Double/TYPE 10000)] (time (doseq [i (range 100), j (range 100)] (aget a (int (+ i (* j 100)))))) (time (doseq [i (range 100), j (range 100)] (aget b (int (+ i (* j 100))))))) Also... is there any way to get (aget a i j) to be fast - or do I have to go with a flat array and calc the offsets? Btw looks like a small bit of markup leaked into your code on the new site: "..." It doesn't appear on the old site. Very interesting!

Sadly this trick doesn’t seem to work for arrays of primitives, or my syntax is wrong?

(let [a (make-array Double/TYPE 10000)
b #^doubles (make-array Double/TYPE 10000)]
(time (doseq [i (range 100), j (range 100)] (aget a (int (+ i (* j 100))))))
(time (doseq [i (range 100), j (range 100)] (aget b (int (+ i (* j 100)))))))

Also… is there any way to get (aget a i j) to be fast – or do I have to go with a flat array and calc the offsets?

Btw looks like a small bit of markup leaked into your code on the new site:
“…”
It doesn’t appear on the old site.

]]>