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std::ispow2

From cppreference.com
< cpp‎ | numeric
Defined in header <bit>
template< class T >
constexpr bool ispow2(T x) noexcept;
(since C++20)

Checks if x is an integral power of two.

This overload only participates in overload resolution 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] Return value

true if x is an integral power of two; otherwise false.

[edit] Possible implementation

template <std::unsigned_integral T>
    requires !std::same_as<T, bool> && !std::same_as<T, char>
constexpr bool ispow2(T x) noexcept
{
    return x != 0 && (x & (x - 1)) == 0;
}

[edit] Example

#include <bit>
#include <iostream>
 
int main()
{
    std::cout << std::boolalpha;
    for (auto i = 0u; i < 10u; ++i) {
        std::cout << "ispow2(" << i << ") = " << std::ispow2(i) << '\n';
    }
}

Output:

ispow2(0) = false
ispow2(1) = true
ispow2(2) = true
ispow2(3) = false
ispow2(4) = true
ispow2(5) = false
ispow2(6) = false
ispow2(7) = false
ispow2(8) = true
ispow2(9) = false