C++ __builtin_popcount() Function

__builtin_popcount()  is a built-in function of GCC compiler. This function is used to count the number of set bits in an unsigned integer. 

Syntax:

__builtin_popcount(int number);

Parameter: This function only takes unsigned or positive integers as a parameter.

Time Complexity:O(1)

Auxiliary Space: O(1)

Input: n = 4
binary value of 4: 100
Output: 1

Example:

C++

// C++ code to demonstrate the
// __builtin_popcount function
#include <bits/stdc++.h>

using namespace std;

int main()
{

    int n = 4;

    // Printing the number of set bits in n
    cout << __builtin_popcount(n);

    return 0;
}

Output

1

What will happen if the data type is of type long long?

__builtin_popcountll is a GCC extension that is used to count the number of set bits in long long data types. 

Syntax:

__builtin_popcountll(long long number);

Example:

C++

// C++ code to demonstrate the
// __builtin_popcount function
#include <bits/stdc++.h>

using namespace std;

int main()
{

    long long n = 1e15;

    // Printing the number of set bits in n
    cout << __builtin_popcountll(n);

    return 0;
}

Output

20

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