std::countl_one

 

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popcount (C++20)

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Defined in header <bit>
template<class T> constexpr int countl_one(T x) noexcept;		(since C++20)

Returns the number of consecutive 1 ("one") bits in the value of x, starting from the most significant bit ("left").

This overload participates in overload resolution only 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).

Parameters

x

-

values of unsigned integer type

Return value

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

Example

Run this code

#include <bit>
#include <bitset>
#include <cstdint>
#include <initializer_list>
#include <iostream>
 
int main()
{
    for (std::uint8_t i : { 0, 0b11111111, 0b11100011 }) {
        std::cout << "countl_one(0b" << std::bitset<8>(i) << ") = "
                  << std::countl_one(i) << '\n';
    }
}

Output:

countl_one(0b00000000) = 0
countl_one(0b11111111) = 8
countl_one(0b11100011) = 3

See also

countl_zero (C++20)	counts the number of consecutive 0 bits, starting from the most significant bit (function template)
countr_zero (C++20)	counts the number of consecutive 0 bits, starting from the least significant bit (function template)
countr_one (C++20)	counts the number of consecutive 1 bits, starting from the least significant bit (function template)
popcount (C++20)	counts the number of 1 bits in an unsigned integer (function template)