hash.h

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#pragma once
 
#include <functional>
#include <span>
#include <cstddef>
#include <filesystem>
#include <string>
#include <string_view>
#include <type_traits>
 
#include <rex/types.h>
#include <rex/platform.h>
 
namespace rex {

template <typename Key>
struct IdentityHasher {
  size_t operator()(const Key& key) const { return static_cast<size_t>(key); }
};

template <typename Key>
struct KeyHasher {
  size_t operator()(const Key& hashed_key) const {
    return std::hash<std::remove_cvref_t<decltype(hashed_key.key)>>{}(hashed_key.key);
  }
};

REX_API u64 HashXXH3(std::span<const u8> data);

template <typename Key>
struct XXHasher {
  size_t operator()(const Key& key) const {
    return static_cast<size_t>(
        HashXXH3(std::span<const u8>(reinterpret_cast<const u8*>(&key), sizeof(key))));
  }
};

REX_API std::string HashBytes(std::string_view data);

REX_API std::string HashFile(const std::filesystem::path& path);

inline size_t hash_combine(size_t hash) {
  return hash;
}

template <typename T, typename... Ts>
size_t hash_combine(size_t hash, const T& v, const Ts&... vs) {
  std::hash<T> hasher;
  hash ^= hasher(v) + 0x9E3779B9 + (hash << 6) + (hash >> 2);
  return hash_combine(hash, vs...);
}
 
}  // namespace rex