Re: General purpose hashing func in pgbench

	Fabien COELHO wrote:

> Most "permutation" functions are really cryptographic cyphers which are 
> quite expensive, and require powers of two, which is not what is needed. 
> ISTM that there are some constructs to deal with arbitrary sizes based on 
> cryptographic functions, but that would make it too expensive for the 
> purpose.

FWIW, you might have a look at the permuteseq extension:
  https://pgxn.org/dist/permuteseq
It permutes an arbitrary range of 64-bit integers into itself,
with a user-supplied key as the seed.
Outputs are coerced into the desired range by using the
smallest possible power of two for the Feistel cypher's
block size, and then cycle-walking over the results.


Best regards,
-- 
Daniel Vérité
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