Cross-platform deterministic physics with Unity DOTS physics and soft floats

• libm

  8 501 5.5 Rust

  A port of MUSL's libm to Rust.

  

So, fixed-point numbers weren't the solution to the problem either. The next thing I came across was the Rapier physics engine. It promises cross-platform determinism all IEEE 754-2008 compliant platforms. Although it's written in Rust, creating C# bindings was fairly easy, and I could use it in Unity after a few hours. But Rapier is still in early stages of development, which means that (at the time of writing this) it lacked many features, like raycasting, which would have been necessary for my project. Also, it's only deterministic on IEEE 754-2008 compliant platforms. But I couldn't really find any information on which processors support it. Even if I did, I still wanted to have deterministic physics on all platforms, not just on "most of them". But I still wondered does how Rapier achieve cross-platform floating point determinism. Supporting only IEEE 754-2008 compliant platforms is one thing, but the mathematical functions I mentioned above (sqrt, trigonometry, etc.) must also be deterministic. I found out that it uses libm, which implements all of these functions in software. It was primarily designed for embedded systems without FPUs, but it turns out it's also pretty useful for making this part of floating point math deterministic. But after all, the basic mathematical operations of floats are still not deterministic. Unless... How about emulating the behavior of floats in software? It should be possible to write a program that works on the byte representation of a float, doing all operations using integer arithmentic... right?

• SoftFloat

  1 113 0.0 C#

  An implementation of 32 bit floating point arithmetic in C#

Yep! I quickly found a repository that does just that! Here it is: https://github.com/CodesInChaos/SoftFloat And it worked! Except for one thing... It didn't have division implemented. After hours of searching and studying how floats work, I finally managed to implement division. Using it together with libm, it was now possible to have cross-platform deterministic floats, that work (almost) exactly the same way as the regular floats, but they will give the same result everywhere, on every platform, on every processor.

• InfluxDB

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• soft-float-starter-pack

  1 157 0.0 C#

  Software implementation of floating point numbers and operations

My code for the soft floats is available here.

• EntityComponentSystemSamples

  23 6,847 4.8 C#
  

Somehow I cant find the Unity DOTS physics on Github to see what the license is. I found, for example, their DOTS Samples repository, which has a "Unity Companion License", meaning its " royalty-free copyright license to reproduce, prepare derivative works " etc. I would imagine all their github projects are like that. I could even ask on the forums if you would be willing to share the code in case the licence is ok (which I am sure it is judging by Unity's other repos)

• unity-deterministic-physics

  2 458 0.0 C#

  Cross-platform deterministic physics simulation in Unity, using DOTS physics and soft floats

Here it is: https://github.com/Kimbatt/unity-deterministic-physics

• SaaSHub

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