Strange Number/Rounding Issues

[WhiteDragon]

I've been working with small numbers recently, and I've come across this issue:

PHP Code:

echo(0.0009 == 0.0008); // 1 


Seemed like a simple precision issue at first... but:

PHP Code:

echo(0.00091 == 0.00080); // 0
echo(0.00091 == 0.00081); // 0
echo(0.000911 == 0.000812); // 1 


I have no idea what the pattern is, but it is currently giving me a lot of trouble.