How fast we can run 128-bit LCG generator?
If you have a linear congruential random number generator X, then applying X say 8 times is another LCG whose constants are easy to find. If X calculated a series a0, A1.a2 etc. then you can calculate a0 to a7, and then apply Y to all 8 numbers in parallel, assuming this takes a lot less than eight times the effort.
I hope you know how to calculate the same LCG many times without divisions.