`bit::vector` — Bit Counts

These methods count the number of set/unset elements in a bit-vector.

1constexpr std::size_t count()  const;
2constexpr std::size_t count1() const;
3constexpr std::size_t count0() const;
4constexpr bool parity() const;

1: Returns the number of elements in the bit-vector set to 1.
2: Returns the number of elements in the bit-vector set to 1 (synonym for count())
3: Returns the number of elements in the bit-vector set to 0.
4: Returns count() % 2— the number of set elements mod 2.

Example

#include <bit/bit.h>
int main()
{
    auto v1 = bit::vector<>::zeros(5);
    auto v2 = bit::vector<>::checker_board(5);
    auto v3 = bit::vector<>::ones(5);

    std::cout
        << "vector\t\t" << "count1\t" << "count0\t" << "parity\n"
        << v1 << '\t' << v1.count1() << '\t' << v1.count0() << '\t' << v1.parity() << '\n'
        << v2 << '\t' << v2.count1() << '\t' << v2.count0() << '\t' << v2.parity() << '\n'
        << v3 << '\t' << v3.count1() << '\t' << v3.count0() << '\t' << v3.parity() << '\n';
}

Output

vector          count1  count0  parity
[0 0 0 0 0]     0       5       0
[0 1 0 1 0]     2       3       0
[1 1 1 1 1]     5       0       1

See Also