std::has_single_bit
Defined in header <bit> |
||
|---|---|---|
template< class T > constexpr bool has_single_bit( T x ) noexcept; |
(since C++20) |
Checks if x is an integral power of two.
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
true if x is an integral power of two; otherwise false.
Notes
Feature testing macro: __cpp_lib_int_pow2.
Possible implementation
| First version |
|---|
template <std::unsigned_integral T>
requires !std::same_as<T, bool> && !std::same_as<T, char> &&
!std::same_as<T, char8_t> && !std::same_as<T, char16_t> &&
!std::same_as<T, char32_t> && !std::same_as<T, wchar_t>
constexpr bool has_single_bit(T x) noexcept
{
return x != 0 && (x & (x - 1)) == 0;
}
|
| Second version |
template <std::unsigned_integral T>
requires !std::same_as<T, bool> && !std::same_as<T, char> &&
!std::same_as<T, char8_t> && !std::same_as<T, char16_t> &&
!std::same_as<T, char32_t> && !std::same_as<T, wchar_t>
constexpr bool has_single_bit(T x) noexcept
{
return std::popcount(x) == 1;
}
|
Example
#include <bit>
#include <bitset>
#include <iostream>
int main()
{
std::cout << std::boolalpha;
for (auto i = 0u; i < 10u; ++i) {
std::cout << "has_single_bit( " << std::bitset<4>(i) << " ) = "
<< std::has_single_bit(i) // `ispow2` before P1956R1
<< '\n';
}
}
Output:
has_single_bit( 0000 ) = false has_single_bit( 0001 ) = true has_single_bit( 0010 ) = true has_single_bit( 0011 ) = false has_single_bit( 0100 ) = true has_single_bit( 0101 ) = false has_single_bit( 0110 ) = false has_single_bit( 0111 ) = false has_single_bit( 1000 ) = true has_single_bit( 1001 ) = false
See also
|
(C++20)
|
counts the number of 1 bits in an unsigned integer (function template) |
returns the number of bits set to true (public member function of std::bitset<N>) |
|
| accesses specific bit (public member function of std::bitset<N>) |
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