Getting some really unexpected number issues that I'm fairly sure I shouldn't be having!

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Simple things like rotating sprites, looking up ATan values, and my usual smooth offset values, are all slightly askew.
I'm not 100% sure whether this is my own damn fault for having coded all my math functions incorrectly, or maybe some weird quirk that I've "gotten used to" in all of Mark's languages, which C++ handles slightly differently.
Either way, I'm doing an awful lot of debugging for things that should be second nature.

Last night, it was all about scrolling a tilemap, which I'm sure you all know I'm perfectly good at doing. But .. It felt like I had to invert all my Y values for some strange reason.
I'm really baffled by this, and will be looking deeper into it, tonight, perhaps coding an identical test engine in both Monkey and C++ to try and figure out exactly what's going wrong, and where.

Also, all rotated sprites on the 3DS seem to need an extra 90 degrees added on. But the exact same code on the PC doesn't.
So weird!!