I took a look at a spigot algorithm[1]. I still think it needs arbitrary precision arithmetics but maybe I miss something obvious.

[1] https://en.wikipedia.org/wiki/Bailey%E2%80%93Borwein%E2%80%9...

Here's an example if you want to try http://www.benzedrine.ch/pi-spigot.c

This doesn't look like a spigot algorithm. It has a link in the comments[1], it calculates the digits of PI from the beginning. The code you linked seems to implement the exact same algorithm.

I don't fully comprehend the code still, but the SCALE parameter suggest that it handles the elements of the array as a fixed point representation of real numbers. I wonder if it's correct for large number of digits.

[1] http://www.codecodex.com/wiki/Calculate_digits_of_pi#C

Wow, this blew my mind. And it's so simple, too.

    def nthHexDigitOfPI(n):
        return 4/(8*n+1) - 2/(8*n+4) - 1/(8*n+5) - 1/(8*n+6)

What you wrote just returns 0 for a large enough n.

Serves me right for stopping the reading on the first line :)