std::has_single_bit - cppreference.com (original) (raw)

| Defined in header | | | | --------------------------------------------------------------------- | | ------------- | | 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).

Contents

• 1 Parameters
• 2 Return value
• 3 Notes
• 4 Possible implementation
• 5 Example
• 6 See also

[edit] Parameters

[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.

[edit] Possible implementation

template<typename T, typename ... U> concept neither = (<T, U> && ...);   template concept strict_unsigned_integral = std::unsigned_integral && 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 #include #include #include   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 (function template) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | | returns the number of bits set to true (public member function of std::bitset) [edit] | | | accesses specific bit (public member function of std::bitset) [edit] |