Yeah, I was thinking of a C++ implementation. The nested for loops get optimized very well for the 3-opt case. There's also a couple of tricks one can do with preloading (simd) of distances for evaluating 2,3-opt simultaneously. That all fits into 200 lines of code. There's also the fact that after executing the best moves there's a lot of previously evaluated moves that are still valid. This also fits into those 200 lines.

Not trivial, but IMO less trivial than self-organizing maps.