对 2^{61}-1 快速取模

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template <typename T>
constexpr uint64_t mod(T res) {
    constexpr uint64_t mod_p = (1ull << 61) - 1;
    res = (res >> 61) + (res & mod_p);
    res = (res >> 61) + (res & mod_p);

    if (res == mod_p) {
        return 0;
    }
    return res;
}