How can I test whether a number is a power of 2?

by

(n & (n - 1)) == 0 is best. However, note that it will incorrectly return true for n=0, so if that is possible, you will want to check for it explicitly.

http://www.graphics.stanford.edu/~seander/bithacks.html has a large collection of clever bit-twiddling algorithms, including this one.

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