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std::has_single_bit(3) C++ Standard Libary std::has_single_bit(3) NAME std::has_single_bit - std::has_single_bit Synopsis Defined in header <bit> template< class T > (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). Parameters x - value of unsigned integer type Return value true if x is an integral power of two; otherwise false. Notes Feature-test macro Value Std Feature __cpp_lib_int_pow2 202002L (C++20) Integral power-of-2 operations 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 && !(x & (x - 1)); } 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 // Run this code #include <bit> #include <bitset> #include <cmath> #include <iostream> int main() { for (auto u = 0u; u != 10; ++u) { std::cout << "u = " << u << " = " << std::bitset<4>(u); if (std::has_single_bit(u)) // `ispow2` before P1956R1 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 See also popcount counts the number of 1 bits in an unsigned integer (C++20) (function template) count returns the number of bits set to true (public member function of std::bitset<N>) test accesses specific bit (public member function of std::bitset<N>) http://cppreference.com 2024.06.10 std::has_single_bit(3)
NAME | Synopsis | Parameters | Return value | Notes | Possible implementation | First version | Second version | Example | Output: | See also
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