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nt factor FASTER primes (was: Re: Code and Perf. Data for Prime Finders (was: Genuine Eratosthenes sieve)) (1 viewing) (1) Guests

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TOPIC: nt factor FASTER primes (was: Re: Code and Perf. Data for Prime Finders (was: Genuine Eratosthenes sieve))

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Will Ness (Visitor)

nt factor FASTER primes (was: Re: Code and Perf. Data for Prime Finders (was: Genuine Eratosthenes sieve))

Daniel Fischer <daniel.is.fischer <at web.de writes: But there's a lot of list constructuion and deconstruction necessary for the Euler sieve. yes. Unless, of course, s smart compiler recognizes there's only one consumer for the values each multiples-list is producing, and keeps it stripped down to a generator function, and its current value. I keep thinkig a smart compiler could eliminate all these span calls and replace them with just some pointers manipulating... Of course I'm no smart compiler, but I don't see how it could be even possible to replace the span calls with pointer manipulation when dealing with lazily generated (infinite, if we're really mean) lists. Even when you're dealing only with strict finite lists, it's not trivial to do efficiently. I keep thinking that storage duplication with span, filter etc. is not really necessary, and can be replaced with some pointer chasing - especially when there's only one consumer present for the generated values. What I mean is thinking of lists in terms of produce/consumer paradigm, as _object_s supporting the { pull, peek } interface, keeping the generator inside that would produce the next value on 'pull' request and keep it ready for any 'peek's. Euler's sieve is sieve (p

s) xs = h ++ sieve ps (t `minus` map (p*) [p,p+2..]) where (h,t) = span (< p*p) xs Everything lives only through access, so (sieve (tail primes) [5,7]) would create an _object_ with the generator which has the 'span' logic inlined: sieve ps xs = make producer such that p := pull ps

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