[bit.count]

Returns: The number of consecutive 0 bits in the value of x, starting from the most significant bit.

[Note 1:

Returns N if x == 0.

— end note]

template<class T>
  constexpr int countl_one(T x) noexcept;

Returns: The number of consecutive 1 bits in the value of x, starting from the most significant bit.

[Note 2:

Returns N if x == numeric_limits<T>::max().

— end note]

template<class T>
  constexpr int countr_zero(T x) noexcept;

Returns: The number of consecutive 0 bits in the value of x, starting from the least significant bit.

[Note 3:

Returns N if x == 0.

— end note]

template<class T>
  constexpr int countr_one(T x) noexcept;

Returns: The number of consecutive 1 bits in the value of x, starting from the least significant bit.

[Note 4:

Returns N if x == numeric_limits<T>::max().

— end note]

template<class T>
  constexpr int popcount(T x) noexcept;

Returns: The number of 1 bits in the value of x.