Difference between revisions of "cpp/numeric/popcount"
From cppreference.com
m (Added the etymology ;-)) |
m (fmt.) |
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===Notes=== | ===Notes=== | ||
| − | {{ | + | The name {{tt|popcount}} is a contraction for "population count". |
| − | + | ||
| − | === Example === | + | {{feature test macro|__cpp_lib_bitops|std=C++20|value=201907L|[[cpp/numeric#Bit manipulation (since C++20)|Bit operations]]}} |
| + | |||
| + | ===Example=== | ||
{{example | {{example | ||
|code= | |code= | ||
| Line 29: | Line 30: | ||
#include <cstdint> | #include <cstdint> | ||
#include <iostream> | #include <iostream> | ||
| + | |||
| + | static_assert(std::popcount(0xFULL) == 4); | ||
int main() | int main() | ||
{ | { | ||
| − | for (const std::uint8_t | + | for (const std::uint8_t x : {0, 0b00011101, 0b11111111}) |
| − | std::cout << "popcount( " << std::bitset<8>( | + | std::cout << "popcount( " << std::bitset<8>(x) << " ) = " |
| − | << std::popcount( | + | << std::popcount(x) << '\n'; |
} | } | ||
|output= | |output= | ||
popcount( 00000000 ) = 0 | popcount( 00000000 ) = 0 | ||
| − | |||
popcount( 00011101 ) = 4 | popcount( 00011101 ) = 4 | ||
| + | popcount( 11111111 ) = 8 | ||
}} | }} | ||
Revision as of 07:20, 31 August 2023
| 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.
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).
Contents |
Parameters
| x | - | value of unsigned integer type |
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) |
| (C++20) |
counts the number of consecutive 1 bits, starting from the most significant bit (function template) |
| (C++20) |
counts the number of consecutive 0 bits, starting from the least significant bit (function template) |
| (C++20) |
counts the number of consecutive 1 bits, starting from the least significant bit (function template) |
| (C++20) |
checks if a number is an integral power of 2 (function template) |
| returns the number of bits set to true (public member function of std::bitset<N>)
| |
| checks if all, any or none of the bits are set to true (public member function of std::bitset<N>)
|
