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

[Lennart Augustsson]

A double has 53 bits in the mantissa which means that for a running
time of about 24 hours you'd still have picoseconds.  I doubt anyone
cares about picoseconds when the running time is a day.
That's why I think a Double is a good choice, it adapts to the time
scale involved.

  -- Lennart

On Sun, Jan 11, 2009 at 4:03 PM, Peter Verswyvelen <bugfact at gmail.com> wrote:
> 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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