hash.h

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/*
  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
*/
 
// Common file for a few small hashing helpers to store things in
// std::unordered_*
 
#ifndef FTAG_HASH_H
#define FTAG_HASH_H
 
namespace FlavorTagInference {
 
  template<typename T>
  std::size_t getHash(const T& obj) {
    return std::hash<T>{}(obj);
  }
 
  // stolen from https://stackoverflow.com/a/27952689
  //
  // it doesn't have to be good, this isn't called much
  //
  inline size_t combine( size_t lhs, size_t rhs ) {
    lhs ^= rhs + 0x517cc1b727220a95 + (lhs << 6) + (lhs >> 2);
    return lhs;
  }
  namespace NNHashing {
    struct NNKey {
      std::string path;
      GNNOptions opts;
      bool operator==(const NNKey& key) const {
        return path == key.path && opts == key.opts;
      }
      std::size_t hash() const {
        return combine(getHash(path), getHash(opts));
      }
    };
 
    struct NNHasher {
      std::size_t operator()(const NNKey& o) const {
        return o.hash();
      }
    };
  }
}
 
#endif