The new bit-shifting seems to be functioning as expected in the save file.

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Today I need to do some extra testing to be super sure, but as far as I can tell, I should now be able to fit 8 times as many levels into the "Online Levels" file without the game getting all freaked out.
A stress test on the 3DS will also be required, because.. I don't trust my own code!!
32-bit integers can be complicated, sometimes, with some systems storing them backwards (Endian), and others dealing with signed or unsigned values.

I'm not 100% sure how that might impact the bit shifting that I'm doing, so I'll need to double check everything's working correctly, and that it can cope in all scenarios.

But it's, for the most part, done. And the game can now store "complete" values for more than 400,000 levels. Yeay!
That really oughta be enough levels!

Next, I need to start work on the online component.
Eeek!