Power of Two - The Idea

Powers of two in binary have exactly one bit set. For example: $1 = 0001_2$, $2 = 0010_2$, $4 = 0100_2$, $8 = 1000_2$. All other numbers have multiple bits set or zero bits.

If $n$ is a power of two, then $n - 1$ flips all bits after the single set bit. For $n = 8 = 1000_2$, $n - 1 = 7 = 0111_2$. Notice $n \land (n - 1) = 0000_2 = 0$.

The boolean condition: n > 0 && (n & (n - 1)) == 0. The first part handles negative numbers and zero. The second checks the bit pattern. Both must be true.