Re: pgbench - add pseudo-random permutation function

Hello Hironobu-san,

Here is a v4, based on our out-of-list discussion:
- the mask function is factored out
- the popcount builtin is used if available

> Attached a v3, based on your fix, plus some additional changes:
> - explicitly declare unsigned variables where appropriate, to avoid casts
> - use smaller 24 bits primes instead of 27-29 bits
> - add a shortcut for multiplier below 24 bits and y value below 40 bits,
> which should avoid the manually implemented multiplication in most
> practical cases (tables with over 2^40 rows are pretty rare...).
> - change the existing shortcut to look a the number of bits instead of
> using 32 limits.
> - add a test for minimal code coverage with over 40 bits sizes
> - attempt to improve the documentation
> - some comments were updates, hopefully for the better

--
Fabien.