hashing.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2025 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner

// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.

// This library 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
// Lesser General Public License for more details.

// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

#ifndef LIBMESH_HASHING_H
#define LIBMESH_HASHING_H

#include <functional>

namespace libMesh
{
namespace boostcopy
{

inline void hash_combine_impl(std::size_t & seed, std::size_t value)
{
  seed ^= value + 0x9e3779b9 + (seed<<6) + (seed>>2);
}

template <typename T>
inline void hash_combine(std::size_t & seed, const T & value)
{
  using std::hash;
  hash_combine_impl(seed, hash<T>{}(value));
}

}


// Fix for STL laziness
struct hash {
public:
  template <typename T1, typename T2>
  std::size_t operator()(const std::pair<T1, T2> & x) const
  {
    // Hopefully argument-based lookup lets us recurse with this
    using std::hash;

    std::size_t returnval = hash<T1>()(x.first);
    boostcopy::hash_combine(returnval, x.second);

    return returnval;
  }

  template <typename T, std::size_t N>
  std::size_t operator()(const std::array<T, N> & x) const
  {
    // Hopefully argument-based lookup lets us recurse with this
    using std::hash;

    std::size_t returnval = 0;
    for (std::size_t i = 0; i != N; ++i)
      boostcopy::hash_combine(returnval, x[i]);

    return returnval;
  }
};


}

#endif // LIBMESH_HASHING_H