Double factorial and primorial

[Niels Möller]

bodrato at mail.dm.unipi.it writes:

> If we really want a prime_count function in GMP I can write a more clever one

I don't know how important that is. Long-term, I think gmp should at
least export some sieving functionality which us suitable as a building
block for that.

>>> counting the primes in [1,2^34] required half the time of
>>> (sieving and) multiplying all primes in [1,3*2^28].
>>
>> So sieving is a significant part of the work for the primorial function.
>
> Counting primes in [1,3*2^28] is 1/60 than counting in [1,2^34], i.e.
> 1/120 of the time to compute primorial(3*2^28).

Ooops, I didn't notice that you had very different intervals in that
comparison.

Regards,
/Niels

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