splitmix32 is just a fast and simple open source 32 bit PRNG. I'm not overly familiar with its inner workings - I do know that 0x9e3779b9 is derived from the golden ratio, e.g., you can derive:

0x9e3779b9 = 2654435769
Φ - 1 ≈ 2654435769 / 2^32

From my understanding, I think the other two constants were chosen empirically to give desirable random properties to the function and don't represent anything in particular.

Still working on the big update - can't really promise a release date for it yet, but hopefully it'll be worth the wait!