std::countl_one

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Numerics library

Common mathematical functions

Mathematical special functions (C++17)

Mathematical constants (C++20)

Floating-point environment (C++11)

Complex numbers

Numeric arrays

Pseudo-random number generation

Factor operations

gcd (C++17)

lcm (C++17)

Interpolations

midpoint (C++20)

lerp (C++20)

Generic numeric operations

iota (C++11)

ranges::iota (C++23)

accumulate

inner_product

adjacent_difference

partial_sum

reduce (C++17)

transform_reduce (C++17)

inclusive_scan (C++17)

exclusive_scan (C++17)

transform_inclusive_scan (C++17)

transform_exclusive_scan (C++17)

Bit operations

bit_cast (C++20)

byteswap (C++23)

has_single_bit (C++20)

bit_ceil (C++20)

bit_floor (C++20)

bit_width (C++20)

rotl (C++20)

rotr (C++20)

countl_zero (C++20)

countl_one (C++20)

countr_zero (C++20)

countr_one (C++20)

popcount (C++20)

endian (C++20)

 

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

-

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	Value	Std	Comment
__cpp_lib_bitops	201907L	(C++20)	Bit operations

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 (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)
has_single_bit (C++20)	checks if a number is an integral power of two (function template)
count	returns the number of bits set to true (public member function of std::bitset<N>)
allanynone	checks if all, any or none of the bits are set to true (public member function of std::bitset<N>)