[Haskell-cafe] Re: System.CPUTime and picoseconds

[Peter Verswyvelen]

wouldn't a double become less and less precise the longer the process is
running?
so Integer sounds like the only datatype that could work here...

and why not do it like in Windows: make two functions, one that returns the
number of CPU ticks, and another that returns the frequency (number of ticks
per second)... This gives you an API that works for whatever clock speed...




On Sun, Jan 11, 2009 at 11:23 AM, Lennart Augustsson <lennart at augustsson.net
> wrote:

> It was suggested that it should be ns, and I complained that ns would
> be obsolete in a while.
> What I really wanted was a switch to Double (and just using seconds),
> instead we got ps.
> At least ps won't get obsolete in a while.
>
>  -- Lennart
>
> On Sun, Jan 11, 2009 at 12:06 AM, ChrisK <haskell at list.mightyreason.com>
> wrote:
> > Manlio Perillo wrote:
> >>
> >> Hi.
> >>
> >> Just out of curiosity, but why Haskell 98 System.CPUTime library module
> >> uses picoseconds instead of, say, nanoseconds?
> >>
> >> At least on POSIX systems, picoseconds precision is *never* specified.
> >>
> >
> > I have not idea.  But at a guess, I would say that 1 ns is not such a
> small
> > time interval anymore.  The CPU speeds are about 3 GHz, so 0.3 ns per CPU
> > clock. Even the RAM clock in a laptop (e.g. Apple's 17" Mac Pro) is 1066
> > MHz, so the internal there is just under 1 ns.
> >
> > Whoever picked picoseconds has made it possible to talk about a single
> clock
> > interval for hardware like this.
> >
> > --
> > Chris
> >
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