Flex / Flash has a neat feature: doing math for you.

So when you want to know what 0.1 + 0.2 is, you don’t need your calculator, just use flex. The result: 0.30000000000000004.

WTF is that about?

I’m currently trying to find out a fix for this. ATM the only workaround is doing a

var x:Number = 0.1 + 0.2
Math.round(x*10) / 10

How hard is it to add to two numbers and give the correct result?

or of course

var x:Number = (0.1 + 0.2).toFixed(1)

Works for actionscript as well as JavaScript

By the way, it’s not only 0.3 which is causing problems.

Doing a simple for loop reveals the size of this bug:

for(var i = 0; i < 20; i++) {
    trace (i * .3);
}

gives

0
0.3
0.6
0.8999999999999999
1.2
1.5
1.7999999999999998
2.1
2.4
2.6999999999999997
3
3.3
3.5999999999999996
3.9
4.2
4.5
4.8
5.1
5.3999999999999995
5

Hmm… studying it further reveals that it’s not only an actionscript problem. Also Javascript gives these strange results. That tells me that it’s an ECMAScript problem, sinds both languages are based on ECMAScript.

I’ve heard of strange rounding / precision errors, but never knew they were that simple to produce. I really hope that someone at adobe addresses this problem and fixes it for the next release of flash.

It seems to have something to do with the number 3 or .3