Von Neumann's algorithm for simulating a fair coin from a coin which is arbitrarily biased (but with independent throws) has moral analogs for any number of fac

Von Neumann's algorithm for simulating a fair coin from a coin which is arbitrarily biased (but with independent throws) has moral analogs for any number of faces. By using more state you can also extract more data per throw. Pieter Wuille created a table based implementation for a d6: https://gist.github.com/sipa/1913cf8aae565ddad0d1de7f2e9f7f31 https://gist.github.com/sipa/1913cf8aae565ddad0d1de7f2e9f7f3... though it isn't terribly efficient -- extracting only 2.722 bits per 4 roles, instead of the 10.34 which is theoretically possible -- because the table becomes fairly large fairly fast. d20 would be even worse. https://gist.github.com/sipa/1621c40775007f1c27a39b608a765b16 https://gist.github.com/sipa/1621c40775007f1c27a39b608a765b1... is a similar implementation for two sides that extracts more than half the theoretical entropy. If your application wanted uniform d20 throws a table that converted independent but biased d20 throws into unbiased d20 throws would be possible (though like above it would be inefficient unless it were very big.)