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Re: constexpr is really very smart!

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Michael S <already5chosen@yahoo.com> writes:

> On Thu, 19 Dec 2024 00:57:20 -0800
> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>
>> Michael S <already5chosen@yahoo.com> writes:
>>
>>> On Wed, 18 Dec 2024 09:45:38 -0800
>>> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>>>
>>>> Michael S <already5chosen@yahoo.com> writes:
[...]
>>>>> According to my measurement gear, in range 0 to 92 there are few
>>>>> points where [the code I posted] is faster than simple loop, but
>>>>> in majority of cases it is slower.
>>>>
>>>> I'm at a loss to understand how this could happen.  In my own
>>>> measurements, the code shown above runs faster than a simple loop
>>>> in all cases above n > 12, more than twice as fast when n > 17,
>>>> more than three times as fast when n > 42, and going up from
>>>> there.  What might account for these radically different results?
>>>
>>> May be, number of repetitions?
>>> I run the test only once.  That gives relative advantage to smaller
>>> code which is less sensitive to cold ICache and to cold branch
>>> predictors.
>>
>> That's an interesting idea.  Can you also run a measurement where
>> the code is run inside loops?  I think it would be instructive
>> to compare the results under the two approaches.
[...]
>
> I feel that running fib(n) with the same n in loop too unrealistic.
> So I decided to run, at least, with different values of n.

I agree, that is a better choice for a measurement test load.

> Ended up spending about a hour just to build a test bench.
>
> The answer is - in a loop of more than dozen iterations your code is
> indeed faster.  Esp. so for hundred or more iterations.

I'm happy to learn that my instincts were validated here.  And I
also learned something, about the effects of code warmup.  Very
interesting.

> Here is my test bench.  [...]

Thank you for that.  Sadly I am not able to run it because my
test environment is lacking _rdtsc(), and I haven't been able
to find out how to install it.

By the way, I send you an email earlier today.  Did that get to
you?

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constexpr is really very smart! Student Project <student@invalid.invalid> - 2024-12-15 20:20 +0000
  Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-16 11:28 +0200
    Re: constexpr is really very smart! David Brown <david.brown@hesbynett.no> - 2024-12-16 11:18 +0100
      Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-16 13:23 +0200
        Re: constexpr is really very smart! David Brown <david.brown@hesbynett.no> - 2024-12-16 13:43 +0100
          Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-17 11:08 +0200
            Re: constexpr is really very smart! David Brown <david.brown@hesbynett.no> - 2024-12-17 11:10 +0100
        Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-18 03:26 -0800
          Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 14:39 +0200
            Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-18 07:42 -0800
    Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-17 12:54 -0800
      Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 01:33 +0200
        Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 13:51 +0200
          Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-19 00:40 -0800
            Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-20 02:17 +0200
              Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-20 14:59 -0800
                Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-22 00:07 +0200
                Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-22 10:25 -0800
                Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-23 17:47 +0200
                Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-24 05:21 -0800
                Bignum multiplication in Python vs GMP (was: constexpr is really very smart!) Michael S <already5chosen@yahoo.com> - 2024-12-25 11:05 +0200
                Re: Bignum multiplication in Python vs GMP (was: constexpr is really very smart!) Michael S <already5chosen@yahoo.com> - 2024-12-25 13:33 +0200
                Re: Bignum multiplication in Python vs GMP (was: constexpr is really very smart!) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-26 18:54 -0800
                Re: Bignum multiplication in Python vs GMP (was: constexpr is really very smart!) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-26 18:42 -0800
          Re: constexpr is really very smart! Student Project <student@invalid.invalid> - 2024-12-19 19:14 +0000
        Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-18 09:45 -0800
          Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 22:00 +0200
            Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-19 00:57 -0800
              Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-19 23:45 +0200
                Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-20 14:31 -0800
                Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-22 00:14 +0200
                Re: constexpr is really very smart! James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-12-21 17:55 -0500
                Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-22 02:22 +0200
                Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-22 10:33 -0800
                Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-23 00:05 +0200
                Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-22 17:17 -0800
  Re: constexpr is really very smart! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-17 12:20 -0800
    Re: constexpr is really very smart! Student Project <student@invalid.invalid> - 2024-12-18 04:45 +0000
      Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 14:17 +0200

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