[erlang-questions] Erlang arithmetics

黃耀賢 (Yau-Hsien Huang) <>
Sun Oct 31 02:03:18 CET 2010


Hi, Dmitry.

I say "No" to what you're doing. Do not compare the difference of execution
time
between programs in Erlang and in JavaScript. It ought to be on Erlang basis
to
measure efficiency of Erlang, and it ought be on the corresponding basis of
JavaScript
for measuring.

Besides, an Erlang program running on HIPE shares benefits of the
platform. Node.js
depends on the JavaScript engine of some browser. As you know, they
are specific
implementations. You would not discuss how differently those codes work just
about
two specific implementations in the article. You're not doing tests for
either HIPE or
Node.js.

Find general cases to discuss which writing fashion causes an Erlang program
better
than other one in the same language and so does Node.js. Thus, you need test
some
Erlang functions, those perform the same arithmetic computation, and compare
time-
difference between them. And do the same work on JavaScript test. Finally
you could
find how difference of enhancement between some rewriting skill on Erlang
programming
and on JavaScript programming.

-- 

Best Regards.

--- Y-H. H.


On Sat, Oct 30, 2010 at 4:03 PM, Dmitry Demeshchuk <>wrote:

> Greetings.
>
> I'm writing an article comparing Erlang and Node.js and I stumbled
> upon the performance question.
>
> My initial goal was to compare some basic arithmetics speed, like the
> total distance between randomly distributed points. So, I have written
> the following code for Erlang:
>
> =====================================================
>
> -module(arith_speed).
> -export([
>    test/1
> ]).
>
> test(N) ->
>    L = lists:seq(1, N),
>    [{X0, Y0} | Points] = [{random:uniform(1000),
> random:uniform(1000)} || _ <- L],
>    Now = now(),
>    lists:foldl(fun move_to/2, {0, {X0, Y0}}, Points),
>    timer:now_diff(now(), Now).
>
> move_to({X, Y}, {Sum, {X0, Y0}}) ->
>    {Sum + math:sqrt((X - X0) * (X - X0) + (Y - Y0) * (Y - Y0)), {X, Y}}.
>
> ======================================================
>
> and the following code for Node.js:
>
> ======================================================
>
> var a = [];
> for(var i = 0; i < 1000000; i++) {
>    a[i] = {};
>    a[i].x = Math.floor(Math.random() * 1000);
>    a[i].y = Math.floor(Math.random() * 1000);
> }
>
> var sum = 0;
>
> var start = (new Date()).valueOf();
>
> for(var i = 1; i < 1000000; i++) {
>    var prev = a[i-1];
>    sum += Math.sqrt((a[i].x - prev.x) * (a[i].x - prev.x) + (a[i].y -
> prev.y) * (a[i].y - prev.y));
> }
>
> var end = (new Date()).valueOf();
>
> console.log(end - start);
>
> ============================================
>
> There was no special tuning for Erlang and Node, both using the latest
> versions.
> But "arith_speed:test(1000000)." from Erlang console and "node
> test.js" have given me very different results: about 413 milliseconds
> for Erlang and 124 milliseconds for Node. So, the difference was about
> 4 times! I tried to change the total number of points, and the overall
> result remained the same.
>
> Both Erlang and V8 (Google's engine that is used by Node) use IEEE
> 754-2008 implementation, so that's not about float type
> representation. So, for now I have several probable explanations:
>
> 1. I've done something wrong and my tests suck (but that may mean that
> the difference in performance may be even more significant)
> 2. Erlang uses type overflow check on each computation to determine if
> it's time to switch from smallint to bigint.
> 3. Some more reasons that I don't know about or don't consider.
>
> Also, I'm still not sure if this kind of test is good for arithmetics
> comparison. On one side, it uses only pretty basic operations
> (summing, multiplying and square root) but on the other side it may
> involve some special computation mechanisms for Erlang that may slow
> it down.
>
> So, any help in this research is very appreciated. I understand that
> this involves another platform too, but since Erlang appeared to be
> slower I want to start from it first.
>
> Thanks in advance.
>
> --
> Best regards,
> Dmitry Demeshchuk
>
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