hashmap-entry.h

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// Copyright 2016 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef V8_BASE_HASHMAP_ENTRY_H_
#define V8_BASE_HASHMAP_ENTRY_H_
 
#include <cstdint>
#include <type_traits>
 
#include "src/base/memory.h"
 
namespace v8 {
namespace base {
 
// Marker type for hashmaps without a value (i.e. hashsets). These won't
// allocate space for the value in the entry.
struct NoHashMapValue {};
 
// HashMap entries are (key, value, hash) triplets, with a boolean indicating if
// they are an empty entry. Some clients may not need to use the value slot
// (e.g. implementers of sets, where the key is the value), in which case they
// should use NoHashMapValue.
template <typename Key, typename Value>
struct TemplateHashMapEntry {
  static_assert((!std::is_same<Value, NoHashMapValue>::value));
 
  Key key;
  Value value;
  uint32_t hash;  // The full hash value for key
 
  TemplateHashMapEntry(Key key, Value value, uint32_t hash)
      : key(key), value(value), hash(hash), exists_(true) {}
 
  bool exists() const { return exists_; }
 
  void clear() { exists_ = false; }
 
 private:
  bool exists_;
};
 
// Specialization for pointer-valued keys
template <typename Key, typename Value>
struct TemplateHashMapEntry<Key*, Value> {
  static_assert((!std::is_same<Value, NoHashMapValue>::value));
 
  Key* key;
  Value value;
  uint32_t hash;  // The full hash value for key
 
  TemplateHashMapEntry(Key* key, Value value, uint32_t hash)
      : key(key), value(value), hash(hash) {}
 
  bool exists() const { return key != nullptr; }
 
  void clear() { key = nullptr; }
};
 
// Specialization for Address-valued keys
template <typename Value>
struct TemplateHashMapEntry<Address, Value> {
  static_assert((!std::is_same<Value, NoHashMapValue>::value));
 
  Address key;
  Value value;
  uint32_t hash;  // The full hash value for key
 
  TemplateHashMapEntry(Address key, Value value, uint32_t hash)
      : key(key), value(value), hash(hash) {}
 
  bool exists() const { return key != -1u; }
 
  void clear() { key = -1u; }
};
 
// Specialization for no value.
template <typename Key>
struct TemplateHashMapEntry<Key, NoHashMapValue> {
  union {
    Key key;
    NoHashMapValue value;  // Value in union with key to not take up space.
  };
  uint32_t hash;  // The full hash value for key
 
  TemplateHashMapEntry(Key key, NoHashMapValue value, uint32_t hash)
      : key(key), hash(hash), exists_(true) {}
 
  bool exists() const { return exists_; }
 
  void clear() { exists_ = false; }
 
 private:
  bool exists_;
};
 
// Specialization for pointer-valued keys and no value.
template <typename Key>
struct TemplateHashMapEntry<Key*, NoHashMapValue> {
  union {
    Key* key;
    NoHashMapValue value;  // Value in union with key to not take up space.
  };
  uint32_t hash;  // The full hash value for key
 
  TemplateHashMapEntry(Key* key, NoHashMapValue value, uint32_t hash)
      : key(key), hash(hash) {}
 
  bool exists() const { return key != nullptr; }
 
  void clear() { key = nullptr; }
};
 
}  // namespace base
}  // namespace v8
 
#endif  // V8_BASE_HASHMAP_ENTRY_H_