hash.h

/********************************************************************
 * Copyright (C) 2015 Liangliang Nan <liangliang.nan@gmail.com>
 * https://3d.bk.tudelft.nl/liangliang/
 *
 * This file is part of Easy3D. If it is useful in your research/work,
 * I would be grateful if you show your appreciation by citing it:
 * ------------------------------------------------------------------
 *      Liangliang Nan.
 *      Easy3D: a lightweight, easy-to-use, and efficient C++ library
 *      for processing and rendering 3D data.
 *      Journal of Open Source Software, 6(64), 3255, 2021.
 * ------------------------------------------------------------------
 *
 * Easy3D is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License Version 3
 * as published by the Free Software Foundation.
 *
 * Easy3D is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 ********************************************************************/
 
#ifndef EASY3D_CORE_HASH_H
#define EASY3D_CORE_HASH_H
 
 
#include <cstdint>
#include <functional>
 
 
namespace easy3d
{
    // The hash function in Google Optimization Tools
    // https://github.com/google/or-tools/blob/stable/ortools/base/hash.h
 
#if 0
    template<typename T>
    inline void hash_combine(uint64_t &seed, T const& value) {
        static std::hash<T> hasher;
        seed ^= hasher(value) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
 
#else
    template<typename T>
    inline void hash_combine(uint64_t &seed, T const& value) {
        static std::hash<T> hasher;
        uint64_t a = (hasher(value) ^ seed) * 0x9ddfea08eb382d69ULL;
        a ^= (a >> 47);
        uint64_t b = (seed ^ a) * 0x9ddfea08eb382d69ULL;
        b ^= (b >> 47);
        seed = b * 0x9ddfea08eb382d69ULL;
    }
#endif
 
    template <typename FT>
    uint64_t hash(const Vec<2, FT>& value) {
        uint64_t seed(0);
        hash_combine(seed, value.x);
        hash_combine(seed, value.y);
        return seed;
    }
 
    template <typename FT>
    uint64_t hash(const Vec<3, FT>& value) {
        uint64_t seed(0);
        hash_combine(seed, value.x);
        hash_combine(seed, value.y);
        hash_combine(seed, value.z);
        return seed;
    }
 
 
    template <int DIM, typename FT> inline
    uint64_t hash(const Vec<DIM, FT>& value) {
        uint64_t seed(0);
        for (int i=0; i<DIM; ++i)
            hash_combine(seed, value[i]);
        return seed;
    }
 
 
    template<typename Iterator>
    inline uint64_t hash(Iterator first, Iterator last) {
        uint64_t seed(0);
        for (; first != last; ++first) {
            hash_combine(seed, *first);
        }
        return seed;
    }
 
 
    template<typename Iterator>
    inline void hash(uint64_t &seed, Iterator first, Iterator last) {
        for (; first != last; ++first) {
            hash_combine(seed, *first);
        }
    }
 
} // namespace easy3d
 
#endif  // EASY3D_CORE_HASH_H