Re: LuaJIT and Floating Point Determinism
- From: Daurnimator <quae@xxxxxxxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Mon, 13 Jan 2014 12:34:23 -0500
IEEE754 should be completely deterministic
Determinism - if you get the same answer for the same inputs and
actions - is a different beast to algebraic equivalence
Just ensure you do the same things in the same order and you won't
have any problems
On 13 January 2014 12:29, Alex <initrd.gz@xxxxxxxxx> wrote:
> How hard is it to ensure floating point determinism in LuaJIT?
>
> I'm making a game engine in LuaJIT, and I was thinking about making a replay
> system by storing the initial state and user input [1]. In order to use this
> system though, the engine code must be deterministic, and apparently making
> floating point operations deterministic is quite tricky, as algebraically
> equivalent expressions may produce different results (ex. a/b may not equal
> a*(1/b)).
>
> Is it worth trying to ensure floating point determinism in LuaJIT, or do the
> optimizations and trace generation make it too hard or impossible?
>
> [1]
> http://www.gamasutra.com/view/feature/2029/developing_your_own_replay_system.php
>
> --
> Sincerely,
> Alex Parrill
Other related posts:
