I'm not sure why you'd see much slower results there. For reference,
I'm on a Core i7-2720-M (MacbookPro 8,1 13" early 2011), and was using
clojure-1.7-beta3.
Also, I looked at the code you posted and I'm not so sure about your
assumption that Java arrays are slower:
* in load-txt-image_array, you could probably type hint the data var
in the first let binding as ^doubles. With that, you should be able
to get rid of the type hinting throughout the rest of the function.
* In your areduce code you're using a vector to carry the result,
which requires packing and unpacking, which ends up being somewhat
like auto-boxing. Using a loop-recur would allow you to carry over the
min and max separately between steps, something like:
(let [len (alength data)]
(loop [i 0 my-min 0.0 my-max 0.0]
(if (< i len)
(let [v (aget data i)]
(recur (unchecked-inc i) (Math/min my-min v) (Math/max my-max v)))
[my-min my-max])))
(could also use min and max instead of Math/min and Math/max)
* In the "update pixel values" part of the function, you're using a
doseq with a range. That'd cause a sequence of boxed numbers of be
generated. Even though you have a ^double as a type hint, which will
get you out of the boxed math warning, there's still boxing going on
and you'll still first getting a boxed number and then have a cast to
primitive double. For example, if you use this function:
user=> (defn a [] (doseq [i (range 50)] (println (+ ^double i 1.0))))
and use no.disassemble, you'll find byte code like this:
278 checkcast java.lang.Number [131]
281 invokestatic
clojure.lang.RT.uncheckedDoubleCast(java.lang.Object) : double [135]
284 dconst_1
285 invokestatic clojure.lang.Numbers.unchecked_add(double,
double) : double [141]
I'd try using a loop-recur here as well instead of the doseq.
As a sidenote, if haven't looked, you might give Prismatic's hiphip[1]
library a try.
[1] - https://github.com/prismatic/hiphip
On Thu, Jun 11, 2015 at 5:43 AM, Ritchie Cai <ritchie...@gmail.com> wrote:
> Yup. Reflection is issue, I needed type hint.
> However, on another note, I notice that in your first test case, your
> evaluation takes about 3 ms, but on my machine it takes 76 ms. I'm running a
> Xeon CPU at 3.5 GHZ, clojure-1.7-RC1. What could cause such a huge different
> timing?
>
> Thanks.
>
>
> On Wednesday, June 10, 2015 at 8:04:00 PM UTC-5, Steven Yi wrote:
>>
>> As mentioned by Colin and Andy, I would guess it would be some form of
>> boxing and reflection going on. I tried the following:
>>
>> (defn array-max [^doubles arr]
>>
>> (let [len (alength arr)]
>>
>> (loop [m Double/NEGATIVE_INFINITY indx 0]
>>
>> (if (< indx len)
>>
>> (recur (max m (aget arr indx)) (unchecked-inc indx))
>>
>> m))))
>>
>>
>> user=> (let [vs (amap (double-array 1280000) idx ret (Math/random))]
>>
>> (time (array-max vs)))
>>
>> "Elapsed time: 3.719835 msecs"
>>
>>
>> To note, if you check out the source of areduce:
>>
>> user=> (source areduce)
>>
>> (defmacro areduce
>>
>> "Reduces an expression across an array a, using an index named idx,
>>
>> and return value named ret, initialized to init, setting ret to the
>>
>> evaluation of expr at each step, returning ret."
>>
>> {:added "1.0"}
>>
>> [a idx ret init expr]
>>
>> `(let [a# ~a]
>>
>> (loop [~idx 0 ~ret ~init]
>>
>> (if (< ~idx (alength a#))
>>
>> (recur (unchecked-inc ~idx) ~expr)
>>
>> ~ret))))
>>
>>
>> It's just a macro, and so typehinting is going to play a factor. For
>> example, with areduce and a type hint on the array:
>>
>>
>> (defn array-max2 [^doubles arr]
>>
>> (areduce arr idx ret Double/NEGATIVE_INFINITY (max ret (aget arr idx))))
>>
>> user=> (let [vs (amap (double-array 1280000) idx ret (Math/random))] (time
>> (array-max vs)))
>>
>> "Elapsed time: 3.314599 msecs"
>>
>>
>> But with no type hint on arr:
>>
>>
>> (defn array-max2 [arr]
>>
>> (areduce arr idx ret Double/NEGATIVE_INFINITY (max ret (aget arr idx))))
>>
>>
>> user=> (let [vs (amap (double-array 1280000) idx ret (Math/random))] (time
>> (array-max2 vs)))
>>
>> "Elapsed time: 35612.919192 msecs"
>>
>>
>> Without a typehint on the arr argument, I also do get boxed math and
>> reflection warnings:
>>
>>
>> Reflection warning,
>> /private/var/folders/0k/xj_drd990xxf4q99n2bdknrc0000gn/T/form-init1595291808747030463.clj:2:3
>> - call to static method alength on clojure.lang.RT can't be resolved
>> (argument types: unknown).
>>
>> Boxed math warning,
>> /private/var/folders/0k/xj_drd990xxf4q99n2bdknrc0000gn/T/form-init1595291808747030463.clj:2:3
>> - call: public static boolean
>> clojure.lang.Numbers.lt(long,java.lang.Object).
>>
>> Reflection warning,
>> /private/var/folders/0k/xj_drd990xxf4q99n2bdknrc0000gn/T/form-init1595291808747030463.clj:2:58
>> - call to static method aget on clojure.lang.RT can't be resolved (argument
>> types: unknown, int).
>>
>> Boxed math warning,
>> /private/var/folders/0k/xj_drd990xxf4q99n2bdknrc0000gn/T/form-init1595291808747030463.clj:2:49
>> - call: public static java.lang.Object
>> clojure.lang.Numbers.max(double,java.lang.Object).
>>
>> form-init1595291808747030463.clj:2 recur arg for primitive local: ret is
>> not matching primitive, had: Object, needed: double
>>
>> Auto-boxing loop arg: ret
>>
>> Reflection warning,
>> /private/var/folders/0k/xj_drd990xxf4q99n2bdknrc0000gn/T/form-init1595291808747030463.clj:2:3
>> - call to static method alength on clojure.lang.RT can't be resolved
>> (argument types: unknown).
>>
>> Boxed math warning,
>> /private/var/folders/0k/xj_drd990xxf4q99n2bdknrc0000gn/T/form-init1595291808747030463.clj:2:3
>> - call: public static boolean
>> clojure.lang.Numbers.lt(long,java.lang.Object).
>>
>> Reflection warning,
>> /private/var/folders/0k/xj_drd990xxf4q99n2bdknrc0000gn/T/form-init1595291808747030463.clj:2:58
>> - call to static method aget on clojure.lang.RT can't be resolved (argument
>> types: unknown, int).
>>
>> Boxed math warning,
>> /private/var/folders/0k/xj_drd990xxf4q99n2bdknrc0000gn/T/form-init1595291808747030463.clj:2:49
>> - call: public static java.lang.Object
>> clojure.lang.Numbers.max(java.lang.Object,java.lang.Object).
>>
>>
>>
>> On Wednesday, June 10, 2015 at 4:07:09 PM UTC-4, Ritchie Cai wrote:
>>>
>>> I'm working on a java array of double with 1280000 elements. I need the
>>> max and min values of the array. So I initially tried areduce and loop, both
>>> gives runs around 20 seconds. But when try (apply max (vec array)) I get
>>> result under 90 ms.
>>> Can anyone explain why there is such a big difference?
>>> Also if want to iterate large java array like this to do some other
>>> operations, e.g. convolution, what's the best way to go? Is there another
>>> fast way to iterate through array or do I need to convert array into vector?
>>>
>>> Thanks
>>> Ritchie
>>>
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