std::countl_one(3)

NAME
std::countl_one - std::countl_one

Synopsis
   Defined in header <bit>
   template< class T > (since C++20)
   constexpr int countl_one( T x ) noexcept;
   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 - value of unsigned integer type

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

Notes
   Feature-test macro: __cpp_lib_bitops

Example
// Run this code
 #include <bit>
 #include <bitset>
 #include <cstdint>
 #include <iostream>
 int main()
 {
     for (const std::uint8_t i : { 0, 0b11111111, 0b01111111, 0b11100011 }) {
         std::cout << "countl_one( " << std::bitset<8>(i) << " ) = "
                   << std::countl_one(i) << '\n';
     }
 }

Output:
 countl_one( 00000000 ) = 0
 countl_one( 11111111 ) = 8
 countl_one( 01111111 ) = 0
 countl_one( 11100011 ) = 3

See also
   countl_zero counts the number of consecutive 0 bits, starting from the most
   (C++20) significant bit
                  (function template)
   countr_zero counts the number of consecutive 0 bits, starting from the least
   (C++20) significant bit
                  (function template)
   countr_one counts the number of consecutive 1 bits, starting from the least
   (C++20) significant bit
                  (function template)
   popcount counts the number of 1 bits in an unsigned integer
   (C++20) (function template)
   has_single_bit checks if a number is an integral power of two
   (C++20) (function template)
   count returns the number of bits set to true
                  (public member function of std::bitset<N>)
   all
   any checks if all, any or none of the bits are set to true
   none (public member function of std::bitset<N>)
   (C++11)