From: Ulrich Mueller <ulm@gentoo.org>
To: Guilherme Amadio <amadio@gentoo.org>
Cc: gentoo-dev@lists.gentoo.org
Subject: Re: [gentoo-dev] [PATCH] qmail.eclass: simplify is_prime()
Date: Fri, 18 Jun 2021 18:30:05 +0200 [thread overview]
Message-ID: <uv96bi19u@gentoo.org> (raw)
In-Reply-To: <YMuwPrwX/KW0CnJu@gentoo.org> (Guilherme Amadio's message of "Thu, 17 Jun 2021 22:27:42 +0200")
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>>>>> On Thu, 17 Jun 2021, Guilherme Amadio wrote:
> There's actually a much simpler solution to this:
> $ is_prime() { test $(factor $1 | cut -d: -f2 | wc -w) == 1; }
> $ for n in $(seq 0 10); do is_prime $n && echo $n is prime; done
> 2 is prime
> 3 is prime
> 5 is prime
> 7 is prime
> $ time factor 20187319083467888113
> 20187319083467888113: 20187319083467888113
> 0.00
This depends on the actual domain of numbers. If the primes involved
have 20 digits as in your example, then factor should be used of course.
I suspect though that we're talking about small numbers (below 100?)
here, in which case a solution in pure bash would be preferable.
Ulrich
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next prev parent reply other threads:[~2021-06-18 16:30 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-17 15:17 [gentoo-dev] [PATCH] qmail.eclass: simplify is_prime() Rolf Eike Beer
2021-06-17 17:42 ` Peter Stuge
2021-06-17 20:27 ` Guilherme Amadio
2021-06-18 16:30 ` Ulrich Mueller [this message]
2021-06-18 19:10 ` Michael Orlitzky
2021-06-18 19:56 ` Rolf Eike Beer
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