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Karim Belabas on Wed, 28 Dec 2022 17:52:45 +0100
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- To: "Ruud H.G. van Tol" <rvtol@isolution.nl>
- Subject: Re: A022921-code
- From: Karim Belabas <Karim.Belabas@math.u-bordeaux.fr>
- Date: Wed, 28 Dec 2022 17:51:34 +0100
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* Ruud H.G. van Tol [2022-12-28 16:28]:
>
> [ logint(3^(n+1),2) - logint(3^n,2) |n<-[0..98]]
>
> is half as fast as
>
>
>
> but IMO looks ugly.
>
> Is there a both "nice" and fast way to do similar?
Not sure about "nice"; but faster, definitely:
? N = 30000;
? w0 = [logint(3^(n+1),2) - logint(3^n,2) | n<-[0..N]];
time = 767 ms.
? my(n0=logint(3^0,2)); w1 = [-n0 + n0=logint(3^(n+1),2) |n<-[0..N]];
time = 355 ms.
? my(v = [logint(x,2) | x <-powers(3, N+1)]); w = vector(#v-1, i, v[i+1]-v[i]);
time = 20 ms.
? [w == w0, w == w1]
%4 = [1, 1]
Cheers,
K.B.
--
Karim Belabas / U. Bordeaux, vice-président en charge du Numérique
Institut de Mathématiques de Bordeaux UMR 5251 - (+33) 05 40 00 29 77
http://www.math.u-bordeaux.fr/~kbelabas/
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