BLI_hash.hh

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#pragma once

 
#include <memory>
#include <string>
#include <utility>
 
#include "BLI_hash_fwd.hh"
#include "BLI_string_ref.hh"
 
namespace blender {

template<typename T> struct DefaultHash {
  uint64_t operator()(const T &value) const
  {
    if constexpr (std::is_enum_v<T>) {
      /* For enums use the value as hash directly. */
      return uint64_t(value);
    }
    else {
      /* Try to call the `hash()` function on the value. */
      /* If this results in a compiler error, no hash function for the type has been found. */
      return value.hash();
    }
  }
 
  template<typename U> uint64_t operator()(const U &value) const
  {
    /* Try calling the static `T::hash_as(value)` function with the given value. The returned hash
     * should be "compatible" with `T::hash()`. Usually that means that if `value` is converted to
     * `T` its hash does not change. */
    /* If this results in a compiler error, no hash function for the heterogeneous lookup has been
     * found. */
    return T::hash_as(value);
  }
};

template<typename T> struct DefaultHash<const T> {
  uint64_t operator()(const T &value) const
  {
    return DefaultHash<T>{}(value);
  }
};
 
#define TRIVIAL_DEFAULT_INT_HASH(TYPE) \
  template<> struct DefaultHash<TYPE> { \
    uint64_t operator()(TYPE value) const \
    { \
      return uint64_t(value); \
    } \
  }

TRIVIAL_DEFAULT_INT_HASH(int8_t);
TRIVIAL_DEFAULT_INT_HASH(uint8_t);
TRIVIAL_DEFAULT_INT_HASH(int16_t);
TRIVIAL_DEFAULT_INT_HASH(uint16_t);
TRIVIAL_DEFAULT_INT_HASH(int32_t);
TRIVIAL_DEFAULT_INT_HASH(uint32_t);
TRIVIAL_DEFAULT_INT_HASH(int64_t);
TRIVIAL_DEFAULT_INT_HASH(uint64_t);

template<> struct DefaultHash<float> {
  uint64_t operator()(float value) const
  {
    /* Explicit `uint64_t` cast to suppress CPPCHECK warning. */
    return uint64_t(*reinterpret_cast<uint32_t *>(&value));
  }
};
 
template<> struct DefaultHash<double> {
  uint64_t operator()(double value) const
  {
    return *reinterpret_cast<uint64_t *>(&value);
  }
};
 
template<> struct DefaultHash<bool> {
  uint64_t operator()(bool value) const
  {
    return uint64_t((value != false) * 1298191);
  }
};
 
inline uint64_t hash_string(StringRef str)
{
  uint64_t hash = 5381;
  for (char c : str) {
    hash = hash * 33 + c;
  }
  return hash;
}
 
template<> struct DefaultHash<std::string> {
  uint64_t operator()(StringRef value) const
  {
    return hash_string(value);
  }
};
 
template<> struct DefaultHash<StringRef> {
  uint64_t operator()(StringRef value) const
  {
    return hash_string(value);
  }
};
 
template<> struct DefaultHash<StringRefNull> {
  uint64_t operator()(StringRef value) const
  {
    return hash_string(value);
  }
};
 
template<> struct DefaultHash<std::string_view> {
  uint64_t operator()(StringRef value) const
  {
    return hash_string(value);
  }
};

template<typename T> struct DefaultHash<T *> {
  uint64_t operator()(const T *value) const
  {
    uintptr_t ptr = uintptr_t(value);
    uint64_t hash = uint64_t(ptr >> 4);
    return hash;
  }
};
 
namespace detail {
static constexpr std::array<uint64_t, 3> default_hash_factors = {19349669, 83492791, 3632623};
 
template<size_t... I, typename... Args>
inline uint64_t get_default_hash_array(std::index_sequence<I...> /*indices*/, const Args &...args)
{
  static_assert(sizeof...(Args) == sizeof...(I));
  static_assert(sizeof...(Args) <= default_hash_factors.size());
  return (0 ^ ... ^ (default_hash_factors[I] * DefaultHash<std::decay_t<Args>>{}(args)));
}
 
}  // namespace detail
 
template<typename T, typename... Args>
inline uint64_t get_default_hash(const T &v, const Args &...args)
{
  return DefaultHash<std::decay_t<T>>{}(v) ^
         detail::get_default_hash_array(std::make_index_sequence<sizeof...(Args)>(), args...);
}

template<typename T> struct PointerHashes {
  template<typename U> uint64_t operator()(const U &value) const
  {
    return get_default_hash(&*value);
  }
};
 
template<typename T> struct DefaultHash<std::unique_ptr<T>> : public PointerHashes<T> {};
template<typename T> struct DefaultHash<std::shared_ptr<T>> : public PointerHashes<T> {};
 
template<typename T> struct DefaultHash<std::reference_wrapper<T>> {
  uint64_t operator()(const std::reference_wrapper<T> &value) const
  {
    return get_default_hash(value.get());
  }
};
 
template<typename T1, typename T2> struct DefaultHash<std::pair<T1, T2>> {
  uint64_t operator()(const std::pair<T1, T2> &value) const
  {
    return get_default_hash(value.first, value.second);
  }
};
 
}  // namespace blender