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Well, one number I found on the decrease of Direct3D's speed with and without the FPU preserve flag:

with: 560 fps
without: 580 fps

However I think it is a bit beside the point to 'prove' this with numbers since DirectX more or less already chose single precision for us (for a good reason, I trust). Also it seems logical for a 3D API to be faster when using float-s in stead of double-s because twice the data can be pushed to the GPU with the same bandwidth / stored in VRAM. Isn't this the same for OpenGL?

Looking at the performance of double vs float on modern CPU-s should be interesting though. Are double-s faster, slower or the same compared to float-s on 32-bit and 64-bit CPU architecture? What about the CPU-s people are actually using on average at the moment? (to sell games we need to look at what is average on the market, not only to what is top-notch :)


----- Original Message ----- From: "Andras Balogh" <>
To: "Lua list" <>
Sent: Thursday, March 16, 2006 2:51 PM
Subject: Re: ANN: LuaJIT 1.1.0 / Re: Lua x DirectX

I still don't buy this. Give me numbers! Should be easy, right? Set
the flag and read FPS counter! I'd test it myself, but I'm using
OpenGL, and thus never had to change the FPU control word..


Thursday, March 16, 2006, 1:35:08 AM, you wrote:

A google search can also produce pages about the loss of speed when using
the 'preserve FPU' flag, like
(quote: "For games, you typically don't want the performance hit of having
the FP unit working in double-precision.").