Considering ways to take the algorithm and turn it into
OpenCL/Boost::Compute functions/code which would offer
a large speed increase.
Also, if I can figure out how to start from any arbitrary
digit (which is supposed to be possible) then multi-threading
would also give great speedups.
I totally brainfarted and put this->preDigits.size() in the for
loop comparison clause, which gets re-evaluated every loop.
So it was leaving digits on the stack that should have been
printed, causing errors both immediately and down the line.
A.M. Rowsell