Ah, I so long for the days of trying to make simple things like finding primes or digits of pi run fast. I remember making a lazy sieve of Eratosthenes that gave you the first 120 million or so primes in 6s using chez scheme. I later did the same kind of lazy construct for pi digits.

It actually taught me a lot about memory access and reasoning about speed, and also a lot about small things that are beneficial for speed.

12T digits of pi is mind-blowing, and in that short amount of time on pretty standard hardware.