>> Forgot to post the actual values:
>> r = 2563421694876090368
>> r = 2563421694876090365
>> Smells a bit like a precision problem in the workings of pg_erand48(),
>> but as soon as I saw floating point numbers I closed my laptop and ran
>> for the door.
>
> Yup. This test has a touching, but entirely unwarranted, faith in
> pg_erand48() producing bit-for-bit the same values everywhere.
Indeed.
I argued against involving any floats computation on principle, but Dean
was confident it could work, and it did simplify the code, so it did not
look that bad an option.
I see two simple approaches:
(1) use another PRNG inside pgbench, eg Knuth's which was used in some
previous submission and is very simple and IMHO better than the rand48
stuff.
(2) extend pg_*rand48() to provide an unsigned 64 bits out of the 48 bits
state.
Any preference?
--
Fabien.
