@Vincent
thanks for your detailed reply :)
@All
Vinzent Hoefler wrote:
On Wednesday 12 July 2006 11:34, Andreas Berger wrote:
save and restore the floating point unit. I will need to do this for
FPC, so if someone knows how to save and restore the FPU, I would
apreciate the help.
F(X)SAVE/F(X)RSTOR
The X-Versions are more efficient, but only available on newer CPUs.
Now that you mention it, I have used these in the past :). BTW, The X
version is available at what CPU's? Would it be acceptable to use this
for FPC or should I use the normal FSAVE/FRSTOR functions? Does FPC have
a function that tells me what processor I'm running on? In this case I
could optimize.
Ideally I could also discover (via an exception
on first FPU usage?) if a thread needs to save/restore the FPU.
Well, I'd say, this is quite hard to do in an efficient way, because you
need to detect the usage of MMX instructions, too. As you may recall,
Intel decided to implement another brain damaged design and mapped the
MMX registers onto the FPU registers.
I have to dig deep in my memory now, so take the following paragraphs
with caution, I may be wrong (it's just too long ago):
In theory it is possible to do, but only if you have write access to the
EFLAGS register (where you could temporarily set a flag to raise an
exception on MMX usage). But the usual DOS-target means DPMI, which
means privilege level 3 which means: You're just not allowed to fiddle
around with those. IIRC, there's a ring0-mode DPMI-Host available
(should be CWSDPR0.EXE), but this only works in real plain DOS, so the
option to run the program inside a Windows-DOS-Box would be out
completely, I guess.
Depending on your needs this might be ok, but as a general solution for
FPC/GO32V2 this wouldn't be acceptable, I think.
You're right, better not to do this for a general library.
Ok, will be start to write the threads.
Andreas
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