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    std::popcount

    From cppreference.com
     
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    Defined in header <bit> 
    template< class T >
constexpr int popcount( T x ) noexcept;
    		(since C++20)

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

    Parameters

    x - a value whose bits to count
    Type requirements
    T - must be an unsigned integer type (that is, unsigned char, unsigned short, unsigned int, unsigned long, unsigned long long, or an extended unsigned integer type) in order to participate in overload resolution.

    Return value

    The number of 1 bits in the value of x.

    Notes

    The name popcount is a contraction for “population count”.

    Feature-test macro Value Std Feature
    __cpp_lib_bitops 201907L (C++20) Bit operations

    Example

    Run this code
    #include <bit>
#include <bitset>
#include <cstdint>
#include <iostream>

static_assert(std::popcount(0xFULL) == 4);

int main()
{
    for (const std::uint8_t x : {0, 0b00011101, 0b11111111})
        std::cout << "popcount( " << std::bitset<8>(x) << " ) = "
                  << std::popcount(x) << '\n';
}

    Output: 

    popcount( 00000000 ) = 0
popcount( 00011101 ) = 4
popcount( 11111111 ) = 8

    See also

    (C++20)
    		 counts the number of consecutive 0 bits, starting from the most significant bit
    (function template) [edit]
    (C++20)
    		 counts the number of consecutive 1 bits, starting from the most significant bit
    (function template) [edit]
    (C++20)
    		 counts the number of consecutive 0 bits, starting from the least significant bit
    (function template) [edit]
    (C++20)
    		 counts the number of consecutive 1 bits, starting from the least significant bit
    (function template) [edit]
    (C++20)
    		 checks if a number is an integral power of 2
    (function template) [edit]
    		returns the number of bits set to true
    (public member function of std::bitset<N>) [edit]
    		checks if all, any or none of the bits are set to true
    (public member function of std::bitset<N>) [edit]