++I vs I++

[spiderbox.am]

Hi everyone.
I just want to ask one question about the following:

//Version 1.
for(var i:uint = 0; i < 100; ++i)
trace("i = " + i);

//Version 2.
for(var i:uint = 0; i < 100; i++)
trace("i = " + i);

Which version is more correct ?

P.S.
I know the answer, just want to share

[nikefido]

i've always seen i++, so that's what I use.

is one more efficient?

[Voetsjoeba]

There is no "more correct" version in this case. There is a significant difference between i++ and ++i though. i++ will return the value of i and then increment it, while ++i will first increment i and then return its value.

*Wait, if you know the answer, why are you asking us instead of just telling people?

[spiderbox.am]

Well, I just wanted to see opinions and some logic...
Yes, one of this versions is more efficient.

Lets see what is translator doing.
For executing statement (i++) it must do the following steps:

1. COPY the value of variable i to somewhere (for example the reference of this value will be j )

2. Increment the value of variable i and return j.

For executing statement (++i) it must do the following step:
1. Increment the value of variable i and return i !!!.

So NEVER use code like this:
for(var i:uint; i < 100; i++) ...

You are not solving BIG efficienty problem but why i++ instead of ++i.

Have a good day.

[spiderbox.am]

FINALLY we have:

Its more efficient to do ++i, because i++ requires storing an intermediate value, incrementing, and then returning. For good practice, you should do ++i whenever you can, unless your real intended meaning is i++. However, modern compilers will do optimizations that will filter-out useless i++ statements and turn them into the equivalent of ++i.

[Rezmason]

:-P The efficiency of a unary operator should have little influence on its "properness".

I would say i++ is the traditional, classic increment operator in for loops. Using ++i in that context is like making a fashion statement.

[Krilnon]

I guess the ironic part of this thread is that the one talking about efficiency is the one using uints. (unless uint operations have become much faster recently, then all of the irony would be in my post )

[spiderbox.am]

Yes, i++ is traditional for loops, but I think the reason is the following:
if you write for(var i:uint=0; i < 100; i+) compiler will give syntax error, on the other hand it will accept the second version without giving any warnings(for(var i:uint=0; i < 100; +i)) LOL

[wvxvw]

Actually, the fastest way to do it is i+=1 %) (assuming i is int). But, in 99% of all loops you'll be optimizing - this is the last subject to change the difference isn't really worth it

[spiderbox.am]

Originally Posted by wvxvw

Actually, the fastest way to do it is i+=1 %) (assuming i is int). But, in 99% of all loops you'll be optimizing - this is the last subject to change the difference isn't really worth it

Why i += 1 will work faster than i++ ???

[wvxvw]

http://osflash.org/as3_speed_optimizations
Here're few good suggestions on optimization.

And here're few more
http://www.rockonflash.com/blog/?p=63

[spiderbox.am]

Well, I just got AMAZING results for loop operator.


var time1:Number = (new Date()).getTime();

for(var i:uint = 0; i < 100000000; ++i);

var time2:Number = (new Date()).getTime();

trace(time2-time1)

This code outputs ~1115 milliseconds.

BUT LETS SEE WHAT HAPPENED WHEN I CHOSE I+=1

var time1:Number = (new Date()).getTime();

for(var i:uint = 0; i < 100000000; i+=1);

var time2:Number = (new Date()).getTime();

trace(time2-time1)

RESULT IS AMAAAAAZING ~235 milliseconds!!!!!!!

P.S.
About my PC:
Intel Core 2 Duo E6700 , 3Gb RAM

[Jerryscript]

Even faster I believe is:

PHP Code:

var time1:Number = (new Date()).getTime();

for(var i:uint = 100000000; i > 0; --i);

var time2:Number = (new Date()).getTime();

trace(time2 - time1); 


And I think fastest is:

PHP Code:

var time1:Number = (new Date()).getTime();

var i:uint = 100000000;

while(i > 0) { --i;}

var time1:Number = (new Date()).getTime();

trace(time2 - time1); 


Do a search for actionscript optimization and you'll find several threads and blog posts on this subject.

[wvxvw]

Nope this was true for AS2, but in AS3 they made some optimizations for for loops, look at the first link from my previous post. Now while is slowlier than for if for increments (not decrements).

[spiderbox.am]

Originally Posted by Jerryscript

Even faster I believe is:

PHP Code:

var time1:Number = (new Date()).getTime();

for(var i:uint = 100000000; i > 0; --i);

var time2:Number = (new Date()).getTime();

trace(time2 - time1); 


And I think fastest is:

PHP Code:

var time1:Number = (new Date()).getTime();

var i:uint = 100000000;

while(i > 0) { --i;}

var time1:Number = (new Date()).getTime();

trace(time2 - time1); 


Do a search for actionscript optimization and you'll find several threads and blog posts on this subject.

Hey, before posting your ideas you can test it.
I have just checked and both versions took ~1300 milliseconds.

So version with i+=1 ~235 is AMAAAAAZING !!!