HashCombine.h

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#pragma once
 
#include <cstddef>
#include <cstdint>
#include <functional>
 
namespace autopas::utils {
 
template <class T>
std::size_t hashValue(const T &value) {
  if constexpr (requires { std::hash<T>{}(value); }) {
    return std::hash<T>{}(value);
  } else {
    return static_cast<std::size_t>(value);
  }
}
 
template <class... Values_T>
std::size_t hashCombine(const Values_T &...values) {
  static_assert(sizeof(std::size_t) == 8,
                "hashCombine() only supports a 64-bit std::size_t, as the mixing constants are chosen for that width.");
 
  constexpr auto mix = [](std::size_t x) {
    constexpr std::uint64_t m = 0xe9846af9b1a615dULL;
    x ^= x >> 32;
    x *= m;
    x ^= x >> 32;
    x *= m;
    x ^= x >> 28;
    return x;
  };
 
  std::size_t seed = 0;
  ((seed = mix(seed + 0x9e3779b9 + hashValue(values))), ...);
  return seed;
}
 
}  // namespace autopas::utils