Pair.hpp

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// This file is part of INSTINCT, the INS Toolkit for Integrated
// Navigation Concepts and Training by the Institute of Navigation of
// the University of Stuttgart, Germany.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
 
#pragma once
 
#include <cstddef>
#include <utility>
#include <functional>
 
namespace std
{
template<class T1, class T2>
struct hash<std::pair<T1, T2>>
{
    std::size_t operator()(const std::pair<T1, T2>& f) const
    {
        auto hash1 = std::hash<T1>{}(f.first);
        auto hash2 = std::hash<T2>{}(f.second);
 
        if (hash1 != hash2)
        {
            return hash1 ^ hash2 << 1;
        }
 
        // If hash1 == hash2, their XOR is zero.
        return hash1;
    }
};
} // namespace std