UMAP pair + Custom Hash

struct pair_hash {
    template<class T1, class T2>
    size_t operator() (const pair<T1, T2> &p) const {
        return hash<T1>()(p.first)^hash<T2>()(p.second);
    }
};
unordered_map<pair<int,int>,int,pair_hash> match;

struct custom_hash {
    static uint64_t splitmix64 (uint64_t x) {
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator () (uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};
unordered_map<int,int,custom_hash> Map;