Magic has nothing to do with understanding assembly. Magic simply is probably undocumented piece of code (they aren't even self-documenting), that in order to understand you have to ask the author about it. There's no magic if you understand the code right away, or by looking up some reference.

> "Magic" becomes obvious common-sense once you understand.

I fully agree. Packing data into a binary array, popcount with bit fiddling, macros for generics, etc may seem "magic" to some, but they can be useful especially in performance-critical code. Once you understand these "magic", they are just some common pieces in your toolbox. C is a simple language. Learning C plus such "magic" still takes much less time than grasping the entire C++.