I was tempted to move this from the programing area to tech due to the poor choice of titles, but I'll be nice and not. Please put a tittle appropriate for the question, it's confusing and silly to put "AMD SUX" as a tittle. It likely might lead you to NOT getting help from those who can help you also.
What you have is called round off error It's likely more to do with the PHP server than the processor.
Here is the problem.
.1 and .3 and .2 aren't idelically stored in floating point format.
IE .1 might not actually be .1 (1/10) as it's stored OR it could be that subtrating that from .3 multiple times will give you a progressive error.
Notice that -2.7755575615629E-17 is the value. not -2.775
This is a very small negative quantity.
I think it's a precision loss error really floating point is an approximation of the values you are giving the server.
here are some pertinent articles for you to peruse and ponder.
Summary from a Uni,
Microsoft's ideas,
Good link page, and a
VERY detailed explanation of floating point.
Bottom line is.. you've raised a complicated issue.. floating point. It could be the P4 uses extended or quad FP precision internally instead of single or double and that's the difference. Notice the number of significant digits also. Just remember FP does not necessary store EXACTLY .1 so... deal with it
Cyb