Hi, Floating points operations are not deterministic. That means that the same computation can give different results because it has been built with different compilers, with different options. But even running the same binary on a different CPU may give you different results : by default, x86 uses 80 bits internal precision while x86_64 uses 64 bits internal precision, there may have differences in the mathematic library installed on different systems. You can find some explanations here for instance [1].
There is no good way to make portable code (remember that Wormux runs on x86, x86_64, sparc, arm, ...) making deterministic computation. In fact, there are merely 3 solutions : a/ force operations precision in a portable way, but it is not that easy. [2] b/ do not use floating points operation at all. That means relying of fixed point integers or using a deterministic floating point library such as streflop [3] c/ support non deterministic computation. That means that we have to resync from times to times. This is how some other games do [4], of course, we are not the first to face the problem. This is how it works before Wormux 0.9.0 but it was far from perfect since it was hiding some bugs (mostly due to bad use of random generator). From my point of view, we have to re-add synchronizations, at least in release mode. Anyway, what has been done for 0.9.0 was useful and we must find way to not hide bugs with synchronization. Regards, Matt (gentildemon) [1] http://blogs.msdn.com/shawnhar/archive/2009/03/25/is-floating-point-math-deterministic.aspx [2] http://www.christian-seiler.de/projekte/fpmath/ [3] http://nicolas.brodu.numerimoire.net/en/programmation/streflop/index.html [4] http://springrts.com/wiki/Syncing_System _______________________________________________ Wormux-dev mailing list Wormux-dev@gna.org https://mail.gna.org/listinfo/wormux-dev
