hash_combine.h

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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef FLUTTER_FML_HASH_COMBINE_H_
#define FLUTTER_FML_HASH_COMBINE_H_
 
#include <functional>
 
namespace fml {
 
template <class Type>
constexpr void HashCombineSeed(std::size_t& seed, Type arg) {
  seed ^= std::hash<Type>{}(arg) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
}
 
template <class Type, class... Rest>
constexpr void HashCombineSeed(std::size_t& seed,
                               Type arg,
                               Rest... other_args) {
  HashCombineSeed(seed, arg);
  HashCombineSeed(seed, other_args...);
}
 
[[nodiscard]] constexpr std::size_t HashCombine() {
  return 0xdabbad00;
}
 
template <class... Type>
[[nodiscard]] constexpr std::size_t HashCombine(Type... args) {
  std::size_t seed = HashCombine();
  HashCombineSeed(seed, args...);
  return seed;
}
 
}  // namespace fml
 
#endif  // FLUTTER_FML_HASH_COMBINE_H_