Defined in header
template< class T >
constexpr T floor2(T x) noexcept;
x is not zero, calculates the largest integral power of two that is not greater than
x is zero, returns zero.
This overload only participates in overload resolution if
T is an unsigned integer type (that is, unsigned char, unsigned short, unsigned int, unsigned long, unsigned long long, or an extended unsigned integer type).
 Return value
x is zero; otherwise, the largest integral power of two that is not greater than
|This section is incomplete|
Reason: no example