template< class T >
constexpr bool has_single_bit( T x ) noexcept;
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).
true if x is an integral power of two; otherwise false.
[edit] NotesPrior to P1956R1, the proposed name for this function template was ispow2.
template<typename T, typename ... U>
concept neither = (!std::same_as<T, U> && ...);
template<typename T>
concept strict_unsigned_integral = std::unsigned_integral<T> &&
neither<T, bool, char, char8_t, char16_t, char32_t, wchar_t>;
// First version
constexpr bool has_single_bit(strict_unsigned_integral auto x) noexcept
{
return x && !(x & (x - 1));
}
// Second version
constexpr bool has_single_bit(strict_unsigned_integral auto x) noexcept
{
return std::popcount(x) == 1;
}[edit] Example
#include <bit>
#include <bitset>
#include <cmath>
#include <iostream>
int main()
{
for (auto u{0u}; u != 0B1010; ++u)
{
std::cout << "u = " << u << " = " << std::bitset<4>(u);
if (std::has_single_bit(u))
std::cout << " = 2^" << std::log2(u) << " (is power of two)";
std::cout << '\n';
}
}
Output:
u = 0 = 0000 u = 1 = 0001 = 2^0 (is power of two) u = 2 = 0010 = 2^1 (is power of two) u = 3 = 0011 u = 4 = 0100 = 2^2 (is power of two) u = 5 = 0101 u = 6 = 0110 u = 7 = 0111 u = 8 = 1000 = 2^3 (is power of two) u = 9 = 1001[edit] See also counts the number of 1 bits in an unsigned integer
std::bitset<N>) [edit] accesses specific bit
std::bitset<N>) [edit]
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