Geek asks and answers

Why am i = i + 1 faster than i ++?

Check this code in Flash:

var i:int = 0;
for (var j:int = 0; j < 5000000; j++)
{
    i=i+1;
}// use about 300ms.

i = 0;
for (var j:int = 0; j < 5000000; j++)
{
    i++;
}// use about 400ms

i = 0;
for (var j:int = 0; j < 5000000; j++)
{
    ++i;
}// use about 400ms too

Why is it i=i+1faster in ActionScript 3 when it is slower in others?

Sorry, I'm wrong. The above code uses the same time. but if you include it in a function, the result will be different.

var i:int;
var j:int;
var startTime:Number;

function func1():void
{
    i = i + 1;
}

function func2():void
{
    i++;
}

startTime = getTimer();
i = 0;
for (j = 0; j < 10000000; j++)
{
    func1();
}
trace(getTimer() - startTime);//5 times:631,628,641,628,632

startTime = getTimer();
i = 0;
for (j = 0; j < 10000000; j++)
{
    func2();
}
trace(getTimer() - startTime);//5 times:800,814,791,832,777
+5
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6 answers

If your loop is located, this can greatly affect performance. If your loop is inside a function, Flash will perform calculations using local registers. A loop containing i++creates the following operation codes:

000013 inclocal_i (REG_2)  ; increment i 
000015 inclocal_i (REG_3)  ; increment j
000017 getlocal (REG_3)    ; push j onto stack
000018 pushint 5000000     ; push 5000000 onto stack
000020 iflt -12            ; jump backward if less than

A loop containing contains the i = i + 1following:

000013 getlocal (REG_2)    ; push i onto stack
000014 pushbyte 1          ; push 1 onto stack
000016 add                 ; add the two
000017 convert_i           ; coerce to integer
000018 setlocal (REG_2)    ; save i back to register 2
000019 inclocal_i (REG_3)  
000021 getlocal (REG_3)
000022 pushint 5000000
000024 iflt -16

i++ , i = i + 1, inclocal_i , .

, script. Flash . . i++ :

000017 getlocal (REG_0, this)   ; push this onto stack
000018 dup                      ; duplicate it
000019 setlocal (REG_2)         ; save this to register 2
000020 getproperty i            ; get property "i"
000022 increment_i              ; add one to it
000023 setlocal (REG_3)         ; save result to register 3
000024 getlocal (REG_2)         ; get this from register 2
000025 getlocal (REG_3)         ; get value from register 3
000026 setproperty i            ; set property "i"
000028 kill (REG_3)             ; kill register 2
000030 kill (REG_2)             ; kill register 3
000032 getlocal (REG_0, this)   ; do the same thing with j...
000033 dup
000034 setlocal (REG_2)
000035 getproperty j
000037 increment_i
000038 setlocal (REG_3)
000039 getlocal (REG_2)
000040 getlocal (REG_3)
000041 setproperty j
000043 kill (REG_3)
000045 kill (REG_2)
000047 getlocal (REG_0, this)
000048 getproperty j
000050 pushint 5000000
000052 iflt -40

i = i + 1 :

000017 getlocal (REG_0, this)   ; push this onto stack
000018 getlocal (REG_0, this)   ; push this onto stack
000019 getproperty i            ; get property "i"
000021 pushbyte 1               ; push 1 onto stack
000023 add                      ; add the two
000024 initproperty i           ; save result to property "i"
000026 getlocal (REG_0, this)   ; increment j...
000027 dup
000028 setlocal (REG_2)
000029 getproperty j
000031 increment_i
000032 setlocal (REG_3)
000033 getlocal (REG_2)
000034 getlocal (REG_3)
000035 setproperty j
000037 kill (REG_3)
000039 kill (REG_2)
000041 getlocal (REG_0, this)
000042 getproperty j
000044 pushint 5000000
000046 iflt -34
+5

, .

Attempt 1
loop 1: 378
loop 2: 396
loop 3: 382

Attempt 2
loop 1: 380
loop 2: 361
loop 3: 361

Attempt 3
loop 1: 375
loop 2: 373
loop 3: 355

10 . :

Attempt 1
loop 1: 3707
loop 2: 3663
loop 3: 3653

Attempt 2
loop 1: 3722
loop 2: 3632
loop 3: 3711

[TestLoopSpeed.as]

package
{
    import flash.display.Sprite;
    import flash.utils.getTimer;

    public class TestLoopSpeed extends Sprite
    {
        public function TestLoopSpeed()
        {
            var timeNow:Number = getTimer();
            var i:int = 0;

            var startOne:Number = getTimer();
            for (var j:int = 0; j < 5000000; j++)
            {
                i=i+1;
            }
            var endOne:Number = getTimer();


            var startTwo:Number = getTimer();
            i = 0;
            for (var j:int = 0; j < 5000000; j++)
            {
                i++;
            }
            var endTwo:Number = getTimer();

            var startThree:Number = getTimer();
            i = 0;
            for (var j:int = 0; j < 5000000; j++)
            {
                ++i;
            }
            var endThree:Number = getTimer();

            trace("loop 1: " + (endOne - startOne));
            trace("loop 2: " + (endTwo - startTwo));
            trace("loop 3: " + (endThree - startThree));
        }
    }
}

, ++ = + 1; , , i, i. ++ 1 . , , , , , , .

- , , , .

Edit

while while, :

loop 1: 3695
loop 2: 3698
loop 3: 3690
loop 4: 3711

loop 1: 3758
loop 2: 3651
loop 3: 3707
loop 4: 3676

[TestLoopSpeed.as] 

package
{
    import flash.display.Sprite;
    import flash.utils.getTimer;

    public class TestLoopSpeed extends Sprite
    {
        public function TestLoopSpeed()
        {
            var timeNow:Number = getTimer();
            var i:int = 0;

            var startOne:Number = getTimer();
            for (var j:int = 0; j < 50000000; j++)
            {
                i=i+1;
            }
            var endOne:Number = getTimer();


            var startTwo:Number = getTimer();
            i = 0;
            for (var j:int = 0; j < 50000000; j++)
            {
                i++;
            }
            var endTwo:Number = getTimer();

            var startThree:Number = getTimer();
            i = 0;
            for (var j:int = 0; j < 50000000; j++)
            {
                ++i;
            }
            var endThree:Number = getTimer();

            var startFour:Number = getTimer();
            i = 0;
            var j:int = -1;
            while (++j < 50000000)
            {
                ++i;
            }
            var endFour:Number = getTimer();

            trace("loop 1: " + (endOne - startOne));
            trace("loop 2: " + (endTwo - startTwo));
            trace("loop 3: " + (endThree - startThree));
            trace("loop 4: " + (endFour - startFour));
        }
    }
}
+4

++ - , , . . " "

regression actionscript.

+2

, , .

import flash.utils.getTimer;

var t:int = getTimer();
var i:int = 0, j:int = -1;
while (++j < 5000000) {
    i += 1;
}
trace(getTimer()-t)

83 .

0

I suggest i++;using instead ++i;, because it is faster than you mentioned.

Have a look at this good explanation: What is more efficient i ++ or ++ i?

0
source

It also depends on the language. Maby in AS3 $ i = $ i + 1 is faster, in PHP there is $ i ++. But as Almas Adilbek says. ++ $ i is the fastest.

Example

<?php
    $start = microtime();

    $i = 0;
    while($i != 100000)
    {
        $i++;
    }

    $end = microtime();

    echo 'First complete in: ' . ($end - $start);

    $start = microtime();

    $i = 0;
    while($i != 100000)
    {
        $i = $i+1;
    }

    $end = microtime();

    echo 'Second complete in: ' . ($end - $start);

    $start = microtime();

    $i = 0;
    while($i != 100000)
    {
       ++$i;
    }

    $end = microtime();

    echo 'Third complete in: ' . ($end - $start);
?>
0
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