hash.hpp

//
// Copyright (c) 2018-2020 Manuel Pöter.
// Licensed under the MIT License. See LICENSE file in the project root for full license information.
//
 
#ifndef XENIUM_HASH_HPP
#define XENIUM_HASH_HPP
 
#include <xenium/utils.hpp>
 
#include <cstdint>
#include <functional>
 
namespace xenium {
 
using hash_t = std::size_t;
 
template <class Key>
struct hash {
  hash_t operator()(const Key& key) const noexcept { return _hash(key); }
 
private:
  std::hash<Key> _hash;
};
 
template <class Key>
struct hash<Key*> {
  hash_t operator()(const Key* key) const noexcept {
    constexpr auto alignment = std::alignment_of<Key>();
    constexpr auto shift = utils::find_last_bit_set(alignment) - 1;
    auto hash = reinterpret_cast<hash_t>(key);
    assert((hash >> shift) << shift == hash); // we must not loose a bit!
    return hash >> shift;
  }
};
} // namespace xenium
 
#endif