Interesting.

If you got this far, here's a simplistic explanation. This converts the 6 simple inputs into 6-bit binary in [0-63] range decimal, with sense-0 being the highest bit at values of 32. You have to map these values to their bit-reverse premutation, which is as easy as converting it to normal binary with some values swapped. Then it detects if the value has only one 1 bit by checking for 1, 2, 4, 8, 16 and 32 values. If it passes that, it decomposes the value until it hits 0. Every time it subtracts, it will output the index from the ROM it is reading from.