[C++20] isPowerOfTwo

isPowerOfTwo.cpp

#include <bit>
#include <concepts>
#include <stdio.h>

template <std::unsigned_integral T>
inline bool isPowerOfTwo(T x) {
    return std::has_single_bit(x);
}

template <std::signed_integral T>
inline bool isPowerOfTwo(T x) {
    return x > 0 && isPowerOfTwo(static_cast<std::make_unsigned<T>>(x));
}

template <typename T>
bool isPowerOfTwoNaive(T x) {
    if (x <= 0) { return false; }

    while (x > 1) {
        if (x % 2 != 0) {
            return false;
        }
        x /= 2;
    }
    return true;
}

int main()
{
    int errorCount = 0;
    for (uint32_t i = 0; i < 65536; ++i) {
        const bool a = isPowerOfTwo(i);
        const bool b = isPowerOfTwoNaive(i);
        if (a != b) {
            errorCount += 1;
            printf("i = 0x%02x, isPowerOfTwo = %d, isPowerOfTwoNaive = %d\n", i, a, b);
        }
    }
    const bool ok = errorCount == 0;
    return ok ? EXIT_SUCCESS : EXIT_FAILURE;
}