[Haskell-cafe] Re: FASTER primes (was: Re: Code and Perf. Data for Prime Finders (was: Genuine Eratosthenes sieve))

Will Ness will_n48 at yahoo.com
Tue Dec 29 08:58:10 EST 2009

Eugene Kirpichov <ekirpichov <at> gmail.com> writes:

> 2009/12/29 Will Ness <will_n48 <at> yahoo.com>:
> > Daniel Fischer <daniel.is.fischer <at> web.de> writes:
> >
> >>
> >>
> >> Am Dienstag 29 Dezember 2009 04:38:21 schrieb Will Ness:
> >> > Now _this_, when tested as interpreted code in GHCi, runs about 2.5x times
> >> > faster than Priority Queue based code from Melissa O'Neill's ZIP package
> >> > mentioned at the haskellwiki/Prime_Numbers page, with
> >> > about half used memory reported, in producing 10,000 to 300,000 primes.
> >> >
> >> > It is faster than BayerPrimes.hs from the ZIP package too, in the tested
> >> > range, at about 35 lines of code in total.
> >>
> >> That's nice. However, the important criterion is how compiled code (-O2)
> > fares. Do the relations continue to hold? How does it compare to a bitsieve?
> >
> >
> > Haven't gotten to that part yet. :)
> >
> > But why is it more important? Would that not tell us more about the compiler
> > performance than the code itself?
> >
> If you mean "algorithmic complexity", you shouldn't care about a
> difference of 2.5x.

It's not just at one point; the asymptotics are _the_same_ across the range that
I've tested (admittedly, somewhat narrow). I measure local behavior simply as
logBase in base of ratio of problem sizes, of the ratio of run times.

> If you mean "actual performance for a particular task", you should
> measure the performance in realistic conditions. Namely, if you're
> implementing a program that needs efficient generation of primes,
> won't you compile it with -O2?

If I realistically needed primes generated in a real life setting, I'd probably
had to use some C for that. If OTOH we're talking about a tutorial code that is
to be as efficient as possible without loosing it clarity, being a reflection of
essentials of the problem, then any overly complicated advanced Haskell wouldn't
be my choice either. And seeing that this overly-complicated (IMO),
steps-jumping PQ-based code was sold to us as the only "faithful" rendering of
the sieve, I wanted to see for myself whether this really holds water.

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