[gmpi] Re: Reqs final draft
- From: "Didier Dambrin" <didid@xxxxxxxxx>
- To: <gmpi@xxxxxxxxxxxxx>
- Date: Fri, 14 Jan 2005 03:48:24 +0100
Catching exceptions is great.. when you debug your code.
I was only making an example. My point is that the CPU state that GMPI
chooses may not be the state I as an application developer choose. To put
it another way, what if the GMPI state is not one that you the plugin
developer like. Then the host is going to switch the state to the GMPI
state, and then the plugin will change it again (possibly back), then
restore it, followed by the host restoring it again.
Ok but let's be practical here - we're all involved in either hosts or
plugins in this list - we should be able to tell if most hosts/plugins are
using the same FPU flags or not.
Of course the best would be that plugins & hosts are responsible of their
own FPU state, but in practice, it's a shared resource, and it costs CPU to
change it all the time.
Note that the FPU precision can be critical in some cases. There are fast
tricks to truncate floats, and if the precision is not what you expect,
they will just not work. But ok, a plugin that uses them will probably
set the precision itself for safety.
And more: restoring the FPU state is just a matter of setting it when you
know it's a constant. When you don't know, you will first have to read
it. Today's hosts render in smaller & smaller slices (considering the
user always wants a shorter latency), playing with the FPU state all the
time can waste a little CPU - won't be huge, but it's still wasted.
I agree - it is wasted time I want to avoid. I suggest that the host never
have to change the state, and that plugins simply assume that the host
wants the plugin to run in that state, even if it makes the plugin sound
nasty.
Second, if you as the plugin developer really really don't want to run in
the state provided by the host, you only have to test it once per
processing run. If you don't like the state, then you can do the change
and restore. Each subsequent process call you know the state to change to
and the state to restore. No more testing, and lighter weight than the
host version.
that's what I suggest we set a default FPU state for what most people would
like it to be, and then the rest can switch it back & forth before their
processing.
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