Re: ANN: LuaJIT 1.1.0 / Re: Lua x DirectX

["Framework Studios: Hugo" <hugo@...>]

Hi,

I'm using the DirectX9c SDK from Feb. 2006 (the latest). Imho maybe we can 
assume the people behind DirectX have a good reason to do something as 
potentially 'dangerous' to other libraries as setting the FPU to single 
precision.

A google search can also produce pages about the loss of speed when using 
the 'preserve FPU' flag, like 
http://discuss.microsoft.com/SCRIPTS/WA-MSD.EXE?A2=ind0504b&L=directxdev&D=1&P=4524 
(quote: "For games, you typically don't want the performance hit of having 
the FP unit working in double-precision.").

With SSE of course it can be avoided, but what about DX drivers on a CPU 
without SSE? Btw, can 32-bit float-s really benefit from SSE2 over 64-bit 
double-s? Or maybe double-s are faster than float-s on 64-bit CPUs?

So for now I'm sticking with having DirectX setting the (perhaps not so very 
deprecated :) FPU to single precision and prefering float over double in our 
game engine until DirectX itself converts to using double-s.

Anyway, today I got LuaJIT to work, big thanks to Roberto for this tip!

luaconf.h:544
- #if defined(LUA_NUMBER_DOUBLE) && !defined(LUA_ANSI) && !defined(__SSE2__) 
&& \
-     (defined(__i386) || defined (_M_IX86) || defined(__i386__))
+ #if 0

       cheers,
               Hugo

----- Original Message ----- 
From: "SevenThunders" <mattcbro@earthlink.net>
To: <lua@bazar2.conectiva.com.br>
Sent: Thursday, March 16, 2006 6:27 AM
Subject: Re: ANN: LuaJIT 1.1.0


> Although I don't know much about DirectX, it is the SSE2 instructions that
> see a large boost using 32 bit floats, since they can do twice as many
> multiplies per clock cycle.  Moreover if the modern Directx drivers are
> using the CPU I would be surprised if they are not using the more modern 
> SSE
> and SSE2 instructions over the old x86 FPU.  Thus one would never have to
> employ the nasty switch to single precision on the FPU (which probably 
> sucks
> up a lot of clock cycles in it's own right).
>
> Perhaps the question is what version of DirectX are you using?  Actually a
> google search produces this link
> http://blogs.msdn.com/tmiller/archive/2004/06/01/145596.aspx
>
> Tell your DirectX to leave the deprecated FPU alone!
> --
> View this message in context: 
> http://www.nabble.com/ANN%3A-LuaJIT-1.1.0-t1273815.html#a3430294
> Sent from the Lua - General forum at Nabble.com.