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- Subject: Re: [ANN] LuaProfiler 2.0
- From: Chris Marrin <chris@...>
- Date: Wed, 15 Jun 2005 07:11:31 -0700
Glenn Maynard wrote:
On Tue, Jun 14, 2005 at 11:55:39PM -0500, Rici Lake wrote:
On 14-Jun-05, at 7:19 PM, Chris Marrin wrote:
I have gotten recent experience with QueryPerformanceCounter(). I
I find this a bit puzzling. A double has 53 bits of precision. A day
has 86400 seconds; log2 of 86400*3e9 is 47.88; in other words, a double
can accurately represent a number of 3GHz ticks up to a bit over 34
days. After that, it should lose one bit of precision, which should be
barely noticeable. In a year, you would lose less than four bits of
precision. If you are reduced to a precision of 100ms, you are losing
something like 28 bits of precision. This suggests that you were doing
arithmetic with floats rather than doubles; floats have 24 bits of
precision, or 29 less than doubles, which would work out to about the
loss you are reporting.
Just to toss this out:
Are you using D3D, or something else that plays with the FPUCW?
Ahhhh, that explains a lot! Yes, we are using D3D, via Ogre. I remember
on my last project we had a similar problem. My precision is low because
D3D is resetting it to single-precision!!! Oh, well. I need to figure
out how to get Ogre to set D3DCREATE_FPU_PRESERVE.
Thanks! But damn, now I don't have a tricky, subtle problem to solve :-)
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"As a general rule,don't solve puzzles that open portals to Hell"'