Making floating point deterministic cross diffrent platforms/hardware

[Guillaume Piolat via Digitalmars-d-learn]

On Sunday, 20 November 2016 at 19:12:06 UTC, Chainingsolid wrote:
> I planning out a game that has to use a lock step, peer to peer 
> networking model to achieve multiplayer, and thus I need to 
> have any floating point used produce the exact same results, no 
> matter what, aka be completely deterministic. What would I need 
> to do to achieve this?

I think you can roughly have that with ldc, always using SSE and 
the same rounding-mode. If you use the FPU then the excess 
precision will make things diverge.
I've not compared the results across OSes but I get the exact 
same results across 32-bit and 64-bit.

Another way for deterministic FP is to round to a lower 
precision, or used fixed-point/integers.

If you use client prediction, and the server (authoritative) 
sends the correct player position to clients regularly (action 
game), then no determinism is actually needed. Ask Manu who knows 
more about this.