Re: [PATCH 01/16] math128: Introduce various 128bit primitives

[Ingo Molnar]

* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> On Fri, 2012-10-26 at 11:24 +0200, Ingo Molnar wrote:
> 
> > So can we control this by restricting the users and avoiding 
> > the overflow?
> > 
> > A 2^64 result should be a *huge* amount of space already for 
> > just about anything.
> 
> I _think_ something like: dl_runtime * dl_deadline < U64_MAX, 
> might do that. The question is, is this constraint usable? 
> Simplified that boils down to about 4 seconds each, which 
> sounds pretty much ok for most people -- but such statements 
> usually come back to bite you (640kb anybody...).

We could constrain the precision, not the maximum value.

Having a 4 seconds hard limit is one thing, only having 10 nsecs 
precision at 40 seconds is another.

Then the introduction of 128 bit math would be purely optional 
and would address *that* limitation of precision, and only that 
limitation. That way we could gladly skip 128 bit math.

Thanks,

	Ingo
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