On: Ten Ways to Check if an Integer Is a Power Of Two ...

[Jabbles]

And 3 == 2^(log_2(3)).

Clearly we want to know if x is an integer power of 2.

[wnoise → Jabbles]

2^(bitsize) == 0.

Edit: Yes, 1 << bitsize is undefined. But unsigned integers actually do have well-defined semantics on overflow, and multiplying by 2 enough times really does produce zero.

[rcfox → wnoise]

Actually, it's undefined behaviour. http://blog.regehr.org/archives/213

[ot → wnoise]

2^(bitsize) == 2^(bitsize)

If you meant 1 << (bitsize), that's undefined behaviour in C