Магический квадрат

#include <set>
template<typename Type, size_t Rank>
bool magical(Type(&matrix)[Rank][Rank]) {
    auto last = Rank * Rank;
    std::set<Type> tmp;
    auto s = 0u;
    for (const auto &row : matrix) {
        for (const auto value : row) {
            if (value <= 0 || value > Type(last)) return false;
            s += value;
            tmp.insert(value);
        }
    }
    if (s != last * (last + 1) / 2 || tmp.size() < last) return false;
    auto sum = s / Rank;
    auto a = 0u;
    auto b = 0u;
    for (auto i = 0u; i < Rank; ++i) {
        a += matrix[i][i];
        b += matrix[i][Rank - i - 1];
    }
    if (a != sum || b != sum) return false;
    for (auto r = 0u; r < Rank; ++r) {
        a = b = 0u;
        for (auto c = 0u; c < Rank; ++c) {
            a += matrix[r][c];
            b += matrix[c][r];
        }
        if (a != sum || b != sum) return false;
    }
    return true;
}