Is dieharder considered as the industry standard tool for testing randomness? Is it commonly used by experts?

https://www.phy.duke.edu/~rgb/General/dieharder.php

Dieharder works OK, and you can easily install it on Ubuntu as a command-line tool. PractRand and TestU01 are more stringent and give you more knobs to play with.

That can be made shorter:

  x+=x*x+9;

Are you sure you don't mean

  x+=((x*x+9)>>32);

(and does that need the outer parentheses?) I doubt the first passes dieharder, as (if my C isn't too rusty) it alternates between odd and even numbers.

I mean you assign the value of the expression to your result.

e.g:

    uint64_t x = 0;
    ...
    uint32_t y = (x+=x*x+9)>>32;