On 8/6/2011 8:34 PM, bearophile wrote:
Walter:
On 8/6/2011 4:46 PM, bearophile wrote:
Walter is not a lover of that -ffast-math switch.
No, I am not. Few understand the subtleties of IEEE arithmetic, and breaking
IEEE conformance is something very, very few should even consider.
I have read several papers about FP arithmetic, but I am not an expert yet on
them. Both GDC and LDC have compilation switches to perform those unsafe FP
optimizations, so even if you don't like them, most D compilers today have them
optional, and I don't think those switches will be removed.
If you want to simulate a flock of boids (http://en.wikipedia.org/wiki/Boids )
on the screen using D, and you use floating point values to represent their
speed vector, introducing unsafe FP optimizations will not harm so much. Video
games are a significant purpose for D language, and in them FP errors are often
benign (maybe some parts of the game are able to tolerate them and some other
part of the game needs to be compiled with strict FP semantics).
Bye,
bearophile
Floating point determinism can be very important when it comes to
reducing network traffic. If you can achieve it, then you can make sure
all players have the same game state and then only send user input
commands over the network.
Glenn Fiedler has an interesting writeup on it, but I haven't had a
chance to read all of it yet:
http://gafferongames.com/networking-for-game-programmers/floating-point-determinism/
