Re: Implementation of forprime() and unextprime()

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

On Sat, Jan 13, 2024 at 03:37:07AM -0800, Ilya Zakharevich wrote:
> > > This remark is also a tiny bit pointless without giving the HTTP url
> > > to browse…   ⅞ ;―]
> > 
> > I was quite sure you could find it yourself.
> 
> … And I was quite sure you can use my analysis of an older code!

But then why should we both waste time on old code ?

> > Yes, we store the product of all primes < 2^i for all i less than 20,
> > which we can then use for sieving (for factor(,0))
> > 
> > ? for(i=1,1000,factor(random(2^1000),2^18))
> > With 2.15.4
> >   ***   last result computed in 1,865 ms.
> > With 2.16.1
> >   ***   last result computed in 124 ms.
> 
> How interesting!  Thanks!
> 
> Still, this does not explain what is so special about 20…

It used to be primelimit=500000, so we could have picked 19 , but
20 (2^20~10^6) is easier to remember. Also its square is 2^40~10^12.
Memory size have grown, so the extra memory requirement should not be
an issue.

Cheers,
Bill.