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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: __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 // Run this code #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 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 2022.07.31 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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