0.09 + 0.01 = 0.0:
Wow! What a weird PHP bug! Result of 0.09 + 0.01 is… guess what, it is 0.0: (yes, zero dot zero colon).
s6urik@web1:~$ echo ' Other float values looks to be processed correctly: <pre lang="bash">s6urik@web1:~$ echo ' System is running on Amazon EC2 small instance. Here is more info: <pre lang="bash">s6urik@web1:~$ php -v PHP 5.2.4-2ubuntu5.3 with Suhosin-Patch 0.9.6.2 (cli) (built: Jul 23 2008 06:44:49) Copyright (c) 1997-2007 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2007 Zend Technologies s6urik@web1:~$ uname -a Linux web1 2.6.21.7-2.fc8xen #1 SMP Fri Feb 15 12:39:36 EST 2008 i686 GNU/Linux
This bug was successfully reproduced on custom compile of PHP 5.2.6. (latest available version on the moment).
Under Valgrind everything is fine and result of expression equals 0.1 as it should be, it means that this is rather CPU issue than PHP as Derick said.