On Sep 4, 3:17 pm, Jason Moxham <[email protected]> wrote:
> On Friday 04 September 2009 08:33:01 Cactus wrote:
>
> > On Sep 4, 4:58 am, Bill Hart <[email protected]> wrote:
> > > I don't personally like the name mpz_practical_prime_p(). The reason is
> > > that it doesn't mean anything particular to anyone but us.
>
> > I also doubt that it will help to have two differenet functions that
> > appear to do the same job to anyone who is unaware of the subtleties
> > involved.
>
> If the user has an algorithm which requires one function over the other , but
> is not aware of the difference between them , then should they really should
> not be writing anything that sophisticated. Either of the new functions would
> be better than the old one in any case.
Nevertheless I think we should avoid names that are easily
misunderstood and I would initially take this name to mean that primes
are divided into two classes - 'practical primes' and 'impractical
primes' - and that this function returns a practical one - but still a
prime. But in fact it might not be a prime at all :-)
If we are going to use 'probable_prime' for the one that gives
probability bounds, why not call this 'lazy' one 'mpz_likely_prime' -
this is more accurate and will at least encourage the potential user
to ask themselves what the difference between a likely and a probable
prime is (why do these have '_p' on the end anyway?).
> > mpz_is_composite(mpz_t n) that returns 1 if composite or 0 if the
> > test fails (compositeness undetermined).
>
> This may well be how I will implement it , with mpz_practical_prime being a
> macro on top of it. I just did it this way as that is how it is usually
> presented.Some books do point out that it would be better to call probable
> prime tests , composite tests instead. If we do the composite test instead
> then we can return more than just true or false , we could return a "why" ,
> ie a trial divisor or a witness.
That's a good additional point in favour of this solution.
I'd still prefer the macro to be 'mpz_likely_prime' though :-)
Brian
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