Hash.h

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#ifndef PMPL_HASH_H_
#define PMPL_HASH_H_
 
#include <functional>
 
 
namespace std {
 
  template <typename T, typename U>
  struct hash<std::pair<T, U>> {
 
    typedef std::pair<T, U> KeyPair;
 
    static constexpr size_t magicOffset = 0x9e3779b99e3779b9;
 
    size_t operator()(const KeyPair& _key) const noexcept {
      static constexpr std::hash<T> hasher1;
      static constexpr std::hash<U> hasher2;
      auto h1 = hasher1(_key.first),
           h2 = hasher2(_key.second);
      return h2 + magicOffset + (h1 << 6) + (h1 >> 2);
    }
 
  };
 
 
}
 
#endif