[petsc-users] PetscTableCreateHashSize

[Jed Brown]

Satish Balay <balay at mcs.anl.gov> writes:

> On Mon, 9 Jan 2017, Jed Brown wrote:
>
>> Satish Balay <balay at mcs.anl.gov> writes:
>> > Sure - I'm using a crappy algorithm [look-up table] to get
>> > "prime_number_close_to(1.4*sz)" - as I don't know how to generate
>> > these numbers automatically.
>> 
>> FWIW, it only needs to be coprime with PETSC_HASH_FACT.
>
> Not sure I understand - are you saying coprime requirement is easier
> satisfy than a single prime?

Yeah, just don't be a multiple of PETSC_HASH_FACT, which is itself
prime.

> I had switched this code to use double-hasing algorithm - and the
> requirement here is - the table size be a prime number. [so I'm
> attempting to estimate a prime number suitable for the table size]

Why is it not sufficient to be coprime?
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