std::has_single_bit
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has_single_bit
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Defined in header
<bit>
template< class T >
constexpr bool has_single_bit( T x ) noexcept;
(since C++20)
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).
[edit] Parameters
x
-
value of unsigned integer type
[edit] Return value
true if x is an integral power of two; otherwise false.
[edit] Notes
Prior to P1956R1, the proposed name for this function template was ispow2.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_int_pow2 |
202002L |
(C++20) | Integral power-of-2 operations |
[edit] Possible implementation
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
Run this code
#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