runtime/base/hash_set.h - platform/art - Git at Google

 /*
  * Copyright (C) 2014 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #ifndef ART_RUNTIME_BASE_HASH_SET_H_
 #define ART_RUNTIME_BASE_HASH_SET_H_

 #include <functional>
 #include <memory>
 #include <stdint.h>
 #include <utility>

 #include "logging.h"

 namespace art {

 // Returns true if an item is empty.
 template <class T>
 class DefaultEmptyFn {
  public:
   void MakeEmpty(T& item) const {
     item = T();
   }
   bool IsEmpty(const T& item) const {
     return item == T();
   }
 };

 template <class T>
 class DefaultEmptyFn<T*> {
  public:
   void MakeEmpty(T*& item) const {
     item = nullptr;
   }
   bool IsEmpty(const T*& item) const {
     return item == nullptr;
   }
 };

 // Low memory version of a hash set, uses less memory than std::unordered_set since elements aren't
 // boxed. Uses linear probing.
 // EmptyFn needs to implement two functions MakeEmpty(T& item) and IsEmpty(const T& item)
 template <class T, class EmptyFn = DefaultEmptyFn<T>, class HashFn = std::hash<T>,
     class Pred = std::equal_to<T>, class Alloc = std::allocator<T>>
 class HashSet {
  public:
   static constexpr double kDefaultMinLoadFactor = 0.5;
   static constexpr double kDefaultMaxLoadFactor = 0.9;
   static constexpr size_t kMinBuckets = 1000;

   class Iterator {
    public:
     Iterator(const Iterator&) = default;
     Iterator(HashSet* hash_set, size_t index) : hash_set_(hash_set), index_(index) {
     }
     Iterator& operator=(const Iterator&) = default;
     bool operator==(const Iterator& other) const {
       return hash_set_ == other.hash_set_ && index_ == other.index_;
     }
     bool operator!=(const Iterator& other) const {
       return !(*this == other);
     }
     Iterator operator++() {  // Value after modification.
       index_ = NextNonEmptySlot(index_);
       return *this;
     }
     Iterator operator++(int) {
       Iterator temp = *this;
       index_ = NextNonEmptySlot(index_);
       return temp;
     }
     T& operator*() {
       DCHECK(!hash_set_->IsFreeSlot(GetIndex()));
       return hash_set_->ElementForIndex(index_);
     }
     const T& operator*() const {
       DCHECK(!hash_set_->IsFreeSlot(GetIndex()));
       return hash_set_->ElementForIndex(index_);
     }
     T* operator->() {
       return &**this;
     }
     const T* operator->() const {
       return &**this;
     }
     // TODO: Operator -- --(int)

    private:
     HashSet* hash_set_;
     size_t index_;

     size_t GetIndex() const {
       return index_;
     }
     size_t NextNonEmptySlot(size_t index) const {
       const size_t num_buckets = hash_set_->NumBuckets();
       DCHECK_LT(index, num_buckets);
       do {
         ++index;
       } while (index < num_buckets && hash_set_->IsFreeSlot(index));
       return index;
     }

     friend class HashSet;
   };

   void Clear() {
     DeallocateStorage();
     AllocateStorage(1);
     num_elements_ = 0;
     elements_until_expand_ = 0;
   }
   HashSet() : num_elements_(0), num_buckets_(0), data_(nullptr),
       min_load_factor_(kDefaultMinLoadFactor), max_load_factor_(kDefaultMaxLoadFactor) {
     Clear();
   }
   HashSet(const HashSet& other) : num_elements_(0), num_buckets_(0), data_(nullptr) {
     *this = other;
   }
   HashSet(HashSet&& other) : num_elements_(0), num_buckets_(0), data_(nullptr) {
     *this = std::move(other);
   }
   ~HashSet() {
     DeallocateStorage();
   }
   HashSet& operator=(HashSet&& other) {
     std::swap(data_, other.data_);
     std::swap(num_buckets_, other.num_buckets_);
     std::swap(num_elements_, other.num_elements_);
     std::swap(elements_until_expand_, other.elements_until_expand_);
     std::swap(min_load_factor_, other.min_load_factor_);
     std::swap(max_load_factor_, other.max_load_factor_);
     return *this;
   }
   HashSet& operator=(const HashSet& other) {
     DeallocateStorage();
     AllocateStorage(other.NumBuckets());
     for (size_t i = 0; i < num_buckets_; ++i) {
       ElementForIndex(i) = other.data_[i];
     }
     num_elements_ = other.num_elements_;
     elements_until_expand_ = other.elements_until_expand_;
     min_load_factor_ = other.min_load_factor_;
     max_load_factor_ = other.max_load_factor_;
     return *this;
   }
   // Lower case for c++11 for each.
   Iterator begin() {
     Iterator ret(this, 0);
     if (num_buckets_ != 0 && IsFreeSlot(ret.GetIndex())) {
       ++ret;  // Skip all the empty slots.
     }
     return ret;
   }
   // Lower case for c++11 for each.
   Iterator end() {
     return Iterator(this, NumBuckets());
   }
   bool Empty() {
     return begin() == end();
   }
   // Erase algorithm:
   // Make an empty slot where the iterator is pointing.
   // Scan fowards until we hit another empty slot.
   // If an element inbetween doesn't rehash to the range from the current empty slot to the
   // iterator. It must be before the empty slot, in that case we can move it to the empty slot
   // and set the empty slot to be the location we just moved from.
   // Relies on maintaining the invariant that there's no empty slots from the 'ideal' index of an
   // element to its actual location/index.
   Iterator Erase(Iterator it) {
     // empty_index is the index that will become empty.
     size_t empty_index = it.GetIndex();
     DCHECK(!IsFreeSlot(empty_index));
     size_t next_index = empty_index;
     bool filled = false;  // True if we filled the empty index.
     while (true) {
       next_index = NextIndex(next_index);
       T& next_element = ElementForIndex(next_index);
       // If the next element is empty, we are done. Make sure to clear the current empty index.
       if (emptyfn_.IsEmpty(next_element)) {
         emptyfn_.MakeEmpty(ElementForIndex(empty_index));
         break;
       }
       // Otherwise try to see if the next element can fill the current empty index.
       const size_t next_hash = hashfn_(next_element);
       // Calculate the ideal index, if it is within empty_index + 1 to next_index then there is
       // nothing we can do.
       size_t next_ideal_index = IndexForHash(next_hash);
       // Loop around if needed for our check.
       size_t unwrapped_next_index = next_index;
       if (unwrapped_next_index < empty_index) {
         unwrapped_next_index += NumBuckets();
       }
       // Loop around if needed for our check.
       size_t unwrapped_next_ideal_index = next_ideal_index;
       if (unwrapped_next_ideal_index < empty_index) {
         unwrapped_next_ideal_index += NumBuckets();
       }
       if (unwrapped_next_ideal_index <= empty_index ||
           unwrapped_next_ideal_index > unwrapped_next_index) {
         // If the target index isn't within our current range it must have been probed from before
         // the empty index.
         ElementForIndex(empty_index) = std::move(next_element);
         filled = true;  // TODO: Optimize
         empty_index = next_index;
       }
     }
     --num_elements_;
     // If we didn't fill the slot then we need go to the next non free slot.
     if (!filled) {
       ++it;
     }
     return it;
   }
   // Find an element, returns end() if not found.
   // Allows custom K types, example of when this is useful.
   // Set of Class* sorted by name, want to find a class with a name but can't allocate a dummy
   // object in the heap for performance solution.
   template <typename K>
   Iterator Find(const K& element) {
     return FindWithHash(element, hashfn_(element));
   }
   template <typename K>
   Iterator FindWithHash(const K& element, size_t hash) {
     DCHECK_EQ(hashfn_(element), hash);
     size_t index = IndexForHash(hash);
     while (true) {
       T& slot = ElementForIndex(index);
       if (emptyfn_.IsEmpty(slot)) {
         return end();
       }
       if (pred_(slot, element)) {
         return Iterator(this, index);
       }
       index = NextIndex(index);
     }
   }
   // Insert an element, allows duplicates.
   void Insert(const T& element) {
     InsertWithHash(element, hashfn_(element));
   }
   void InsertWithHash(const T& element, size_t hash) {
     DCHECK_EQ(hash, hashfn_(element));
     if (num_elements_ >= elements_until_expand_) {
       Expand();
       DCHECK_LT(num_elements_, elements_until_expand_);
     }
     const size_t index = FirstAvailableSlot(IndexForHash(hash));
     data_[index] = element;
     ++num_elements_;
   }
   size_t Size() const {
     return num_elements_;
   }
   void ShrinkToMaximumLoad() {
     Resize(Size() / max_load_factor_);
   }
   // To distance that inserted elements were probed. Used for measuring how good hash functions
   // are.
   size_t TotalProbeDistance() const {
     size_t total = 0;
     for (size_t i = 0; i < NumBuckets(); ++i) {
       const T& element = ElementForIndex(i);
       if (!emptyfn_.IsEmpty(element)) {
         size_t ideal_location = IndexForHash(hashfn_(element));
         if (ideal_location > i) {
           total += i + NumBuckets() - ideal_location;
         } else {
           total += i - ideal_location;
         }
       }
     }
     return total;
   }
   // Calculate the current load factor and return it.
   double CalculateLoadFactor() const {
     return static_cast<double>(Size()) / static_cast<double>(NumBuckets());
   }
   // Make sure that everything reinserts in the right spot. Returns the number of errors.
   size_t Verify() {
     size_t errors = 0;
     for (size_t i = 0; i < num_buckets_; ++i) {
       T& element = data_[i];
       if (!emptyfn_.IsEmpty(element)) {
         T temp;
         emptyfn_.MakeEmpty(temp);
         std::swap(temp, element);
         size_t first_slot = FirstAvailableSlot(IndexForHash(hashfn_(temp)));
         if (i != first_slot) {
           LOG(ERROR) << "Element " << i << " should be in slot " << first_slot;
           ++errors;
         }
         std::swap(temp, element);
       }
     }
     return errors;
   }

  private:
   T& ElementForIndex(size_t index) {
     DCHECK_LT(index, NumBuckets());
     DCHECK(data_ != nullptr);
     return data_[index];
   }
   const T& ElementForIndex(size_t index) const {
     DCHECK_LT(index, NumBuckets());
     DCHECK(data_ != nullptr);
     return data_[index];
   }
   size_t IndexForHash(size_t hash) const {
     return hash % num_buckets_;
   }
   size_t NextIndex(size_t index) const {
     if (UNLIKELY(++index >= num_buckets_)) {
       DCHECK_EQ(index, NumBuckets());
       return 0;
     }
     return index;
   }
   bool IsFreeSlot(size_t index) const {
     return emptyfn_.IsEmpty(ElementForIndex(index));
   }
   size_t NumBuckets() const {
     return num_buckets_;
   }
   // Allocate a number of buckets.
   void AllocateStorage(size_t num_buckets) {
     num_buckets_ = num_buckets;
     data_ = allocfn_.allocate(num_buckets_);
     for (size_t i = 0; i < num_buckets_; ++i) {
       allocfn_.construct(allocfn_.address(data_[i]));
       emptyfn_.MakeEmpty(data_[i]);
     }
   }
   void DeallocateStorage() {
     if (num_buckets_ != 0) {
       for (size_t i = 0; i < NumBuckets(); ++i) {
         allocfn_.destroy(allocfn_.address(data_[i]));
       }
       allocfn_.deallocate(data_, NumBuckets());
       data_ = nullptr;
       num_buckets_ = 0;
     }
   }
   // Expand the set based on the load factors.
   void Expand() {
     size_t min_index = static_cast<size_t>(Size() / min_load_factor_);
     if (min_index < kMinBuckets) {
       min_index = kMinBuckets;
     }
     // Resize based on the minimum load factor.
     Resize(min_index);
     // When we hit elements_until_expand_, we are at the max load factor and must expand again.
     elements_until_expand_ = NumBuckets() * max_load_factor_;
   }
   // Expand / shrink the table to the new specified size.
   void Resize(size_t new_size) {
     DCHECK_GE(new_size, Size());
     T* old_data = data_;
     size_t old_num_buckets = num_buckets_;
     // Reinsert all of the old elements.
     AllocateStorage(new_size);
     for (size_t i = 0; i < old_num_buckets; ++i) {
       T& element = old_data[i];
       if (!emptyfn_.IsEmpty(element)) {
         data_[FirstAvailableSlot(IndexForHash(hashfn_(element)))] = std::move(element);
       }
       allocfn_.destroy(allocfn_.address(element));
     }
     allocfn_.deallocate(old_data, old_num_buckets);
   }
   ALWAYS_INLINE size_t FirstAvailableSlot(size_t index) const {
     while (!emptyfn_.IsEmpty(data_[index])) {
       index = NextIndex(index);
     }
     return index;
   }

   Alloc allocfn_;  // Allocator function.
   HashFn hashfn_;  // Hashing function.
   EmptyFn emptyfn_;  // IsEmpty/SetEmpty function.
   Pred pred_;  // Equals function.
   size_t num_elements_;  // Number of inserted elements.
   size_t num_buckets_;  // Number of hash table buckets.
   size_t elements_until_expand_;  // Maxmimum number of elements until we expand the table.
   T* data_;  // Backing storage.
   double min_load_factor_;
   double max_load_factor_;

   friend class Iterator;
 };

 }  // namespace art

 #endif  // ART_RUNTIME_BASE_HASH_SET_H_
	/*
	* Copyright (C) 2014 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#ifndef ART_RUNTIME_BASE_HASH_SET_H_
	#define ART_RUNTIME_BASE_HASH_SET_H_

	#include <functional>
	#include <memory>
	#include <stdint.h>
	#include <utility>

	#include "logging.h"

	namespace art {

	// Returns true if an item is empty.
	template <class T>
	class DefaultEmptyFn {
	public:
	void MakeEmpty(T& item) const {
	item = T();
	}
	bool IsEmpty(const T& item) const {
	return item == T();
	}
	};

	template <class T>
	class DefaultEmptyFn<T*> {
	public:
	void MakeEmpty(T*& item) const {
	item = nullptr;
	}
	bool IsEmpty(const T*& item) const {
	return item == nullptr;
	}
	};

	// Low memory version of a hash set, uses less memory than std::unordered_set since elements aren't
	// boxed. Uses linear probing.
	// EmptyFn needs to implement two functions MakeEmpty(T& item) and IsEmpty(const T& item)
	template <class T, class EmptyFn = DefaultEmptyFn<T>, class HashFn = std::hash<T>,
	class Pred = std::equal_to<T>, class Alloc = std::allocator<T>>
	class HashSet {
	public:
	static constexpr double kDefaultMinLoadFactor = 0.5;
	static constexpr double kDefaultMaxLoadFactor = 0.9;
	static constexpr size_t kMinBuckets = 1000;

	class Iterator {
	public:
	Iterator(const Iterator&) = default;
	Iterator(HashSet* hash_set, size_t index) : hash_set_(hash_set), index_(index) {
	}
	Iterator& operator=(const Iterator&) = default;
	bool operator==(const Iterator& other) const {
	return hash_set_ == other.hash_set_ && index_ == other.index_;
	}
	bool operator!=(const Iterator& other) const {
	return !(*this == other);
	}
	Iterator operator++() { // Value after modification.
	index_ = NextNonEmptySlot(index_);
	return *this;
	}
	Iterator operator++(int) {
	Iterator temp = *this;
	index_ = NextNonEmptySlot(index_);
	return temp;
	}
	T& operator*() {
	DCHECK(!hash_set_->IsFreeSlot(GetIndex()));
	return hash_set_->ElementForIndex(index_);
	}
	const T& operator*() const {
	DCHECK(!hash_set_->IsFreeSlot(GetIndex()));
	return hash_set_->ElementForIndex(index_);
	}
	T* operator->() {
	return &**this;
	}
	const T* operator->() const {
	return &**this;
	}
	// TODO: Operator -- --(int)

	private:
	HashSet* hash_set_;
	size_t index_;

	size_t GetIndex() const {
	return index_;
	}
	size_t NextNonEmptySlot(size_t index) const {
	const size_t num_buckets = hash_set_->NumBuckets();
	DCHECK_LT(index, num_buckets);
	do {
	++index;
	} while (index < num_buckets && hash_set_->IsFreeSlot(index));
	return index;
	}

	friend class HashSet;
	};

	void Clear() {
	DeallocateStorage();
	AllocateStorage(1);
	num_elements_ = 0;
	elements_until_expand_ = 0;
	}
	HashSet() : num_elements_(0), num_buckets_(0), data_(nullptr),
	min_load_factor_(kDefaultMinLoadFactor), max_load_factor_(kDefaultMaxLoadFactor) {
	Clear();
	}
	HashSet(const HashSet& other) : num_elements_(0), num_buckets_(0), data_(nullptr) {
	*this = other;
	}
	HashSet(HashSet&& other) : num_elements_(0), num_buckets_(0), data_(nullptr) {
	*this = std::move(other);
	}
	~HashSet() {
	DeallocateStorage();
	}
	HashSet& operator=(HashSet&& other) {
	std::swap(data_, other.data_);
	std::swap(num_buckets_, other.num_buckets_);
	std::swap(num_elements_, other.num_elements_);
	std::swap(elements_until_expand_, other.elements_until_expand_);
	std::swap(min_load_factor_, other.min_load_factor_);
	std::swap(max_load_factor_, other.max_load_factor_);
	return *this;
	}
	HashSet& operator=(const HashSet& other) {
	DeallocateStorage();
	AllocateStorage(other.NumBuckets());
	for (size_t i = 0; i < num_buckets_; ++i) {
	ElementForIndex(i) = other.data_[i];
	}
	num_elements_ = other.num_elements_;
	elements_until_expand_ = other.elements_until_expand_;
	min_load_factor_ = other.min_load_factor_;
	max_load_factor_ = other.max_load_factor_;
	return *this;
	}
	// Lower case for c++11 for each.
	Iterator begin() {
	Iterator ret(this, 0);
	if (num_buckets_ != 0 && IsFreeSlot(ret.GetIndex())) {
	++ret; // Skip all the empty slots.
	}
	return ret;
	}
	// Lower case for c++11 for each.
	Iterator end() {
	return Iterator(this, NumBuckets());
	}
	bool Empty() {
	return begin() == end();
	}
	// Erase algorithm:
	// Make an empty slot where the iterator is pointing.
	// Scan fowards until we hit another empty slot.
	// If an element inbetween doesn't rehash to the range from the current empty slot to the
	// iterator. It must be before the empty slot, in that case we can move it to the empty slot
	// and set the empty slot to be the location we just moved from.
	// Relies on maintaining the invariant that there's no empty slots from the 'ideal' index of an
	// element to its actual location/index.
	Iterator Erase(Iterator it) {
	// empty_index is the index that will become empty.
	size_t empty_index = it.GetIndex();
	DCHECK(!IsFreeSlot(empty_index));
	size_t next_index = empty_index;
	bool filled = false; // True if we filled the empty index.
	while (true) {
	next_index = NextIndex(next_index);
	T& next_element = ElementForIndex(next_index);
	// If the next element is empty, we are done. Make sure to clear the current empty index.
	if (emptyfn_.IsEmpty(next_element)) {
	emptyfn_.MakeEmpty(ElementForIndex(empty_index));
	break;
	}
	// Otherwise try to see if the next element can fill the current empty index.
	const size_t next_hash = hashfn_(next_element);
	// Calculate the ideal index, if it is within empty_index + 1 to next_index then there is
	// nothing we can do.
	size_t next_ideal_index = IndexForHash(next_hash);
	// Loop around if needed for our check.
	size_t unwrapped_next_index = next_index;
	if (unwrapped_next_index < empty_index) {
	unwrapped_next_index += NumBuckets();
	}
	// Loop around if needed for our check.
	size_t unwrapped_next_ideal_index = next_ideal_index;
	if (unwrapped_next_ideal_index < empty_index) {
	unwrapped_next_ideal_index += NumBuckets();
	}
	if (unwrapped_next_ideal_index <= empty_index \|\|
	unwrapped_next_ideal_index > unwrapped_next_index) {
	// If the target index isn't within our current range it must have been probed from before
	// the empty index.
	ElementForIndex(empty_index) = std::move(next_element);
	filled = true; // TODO: Optimize
	empty_index = next_index;
	}
	}
	--num_elements_;
	// If we didn't fill the slot then we need go to the next non free slot.
	if (!filled) {
	++it;
	}
	return it;
	}
	// Find an element, returns end() if not found.
	// Allows custom K types, example of when this is useful.
	// Set of Class* sorted by name, want to find a class with a name but can't allocate a dummy
	// object in the heap for performance solution.
	template <typename K>
	Iterator Find(const K& element) {
	return FindWithHash(element, hashfn_(element));
	}
	template <typename K>
	Iterator FindWithHash(const K& element, size_t hash) {
	DCHECK_EQ(hashfn_(element), hash);
	size_t index = IndexForHash(hash);
	while (true) {
	T& slot = ElementForIndex(index);
	if (emptyfn_.IsEmpty(slot)) {
	return end();
	}
	if (pred_(slot, element)) {
	return Iterator(this, index);
	}
	index = NextIndex(index);
	}
	}
	// Insert an element, allows duplicates.
	void Insert(const T& element) {
	InsertWithHash(element, hashfn_(element));
	}
	void InsertWithHash(const T& element, size_t hash) {
	DCHECK_EQ(hash, hashfn_(element));
	if (num_elements_ >= elements_until_expand_) {
	Expand();
	DCHECK_LT(num_elements_, elements_until_expand_);
	}
	const size_t index = FirstAvailableSlot(IndexForHash(hash));
	data_[index] = element;
	++num_elements_;
	}
	size_t Size() const {
	return num_elements_;
	}
	void ShrinkToMaximumLoad() {
	Resize(Size() / max_load_factor_);
	}
	// To distance that inserted elements were probed. Used for measuring how good hash functions
	// are.
	size_t TotalProbeDistance() const {
	size_t total = 0;
	for (size_t i = 0; i < NumBuckets(); ++i) {
	const T& element = ElementForIndex(i);
	if (!emptyfn_.IsEmpty(element)) {
	size_t ideal_location = IndexForHash(hashfn_(element));
	if (ideal_location > i) {
	total += i + NumBuckets() - ideal_location;
	} else {
	total += i - ideal_location;
	}
	}
	}
	return total;
	}
	// Calculate the current load factor and return it.
	double CalculateLoadFactor() const {
	return static_cast<double>(Size()) / static_cast<double>(NumBuckets());
	}
	// Make sure that everything reinserts in the right spot. Returns the number of errors.
	size_t Verify() {
	size_t errors = 0;
	for (size_t i = 0; i < num_buckets_; ++i) {
	T& element = data_[i];
	if (!emptyfn_.IsEmpty(element)) {
	T temp;
	emptyfn_.MakeEmpty(temp);
	std::swap(temp, element);
	size_t first_slot = FirstAvailableSlot(IndexForHash(hashfn_(temp)));
	if (i != first_slot) {
	LOG(ERROR) << "Element " << i << " should be in slot " << first_slot;
	++errors;
	}
	std::swap(temp, element);
	}
	}
	return errors;
	}

	private:
	T& ElementForIndex(size_t index) {
	DCHECK_LT(index, NumBuckets());
	DCHECK(data_ != nullptr);
	return data_[index];
	}
	const T& ElementForIndex(size_t index) const {
	DCHECK_LT(index, NumBuckets());
	DCHECK(data_ != nullptr);
	return data_[index];
	}
	size_t IndexForHash(size_t hash) const {
	return hash % num_buckets_;
	}
	size_t NextIndex(size_t index) const {
	if (UNLIKELY(++index >= num_buckets_)) {
	DCHECK_EQ(index, NumBuckets());
	return 0;
	}
	return index;
	}
	bool IsFreeSlot(size_t index) const {
	return emptyfn_.IsEmpty(ElementForIndex(index));
	}
	size_t NumBuckets() const {
	return num_buckets_;
	}
	// Allocate a number of buckets.
	void AllocateStorage(size_t num_buckets) {
	num_buckets_ = num_buckets;
	data_ = allocfn_.allocate(num_buckets_);
	for (size_t i = 0; i < num_buckets_; ++i) {
	allocfn_.construct(allocfn_.address(data_[i]));
	emptyfn_.MakeEmpty(data_[i]);
	}
	}
	void DeallocateStorage() {
	if (num_buckets_ != 0) {
	for (size_t i = 0; i < NumBuckets(); ++i) {
	allocfn_.destroy(allocfn_.address(data_[i]));
	}
	allocfn_.deallocate(data_, NumBuckets());
	data_ = nullptr;
	num_buckets_ = 0;
	}
	}
	// Expand the set based on the load factors.
	void Expand() {
	size_t min_index = static_cast<size_t>(Size() / min_load_factor_);
	if (min_index < kMinBuckets) {
	min_index = kMinBuckets;
	}
	// Resize based on the minimum load factor.
	Resize(min_index);
	// When we hit elements_until_expand_, we are at the max load factor and must expand again.
	elements_until_expand_ = NumBuckets() * max_load_factor_;
	}
	// Expand / shrink the table to the new specified size.
	void Resize(size_t new_size) {
	DCHECK_GE(new_size, Size());
	T* old_data = data_;
	size_t old_num_buckets = num_buckets_;
	// Reinsert all of the old elements.
	AllocateStorage(new_size);
	for (size_t i = 0; i < old_num_buckets; ++i) {
	T& element = old_data[i];
	if (!emptyfn_.IsEmpty(element)) {
	data_[FirstAvailableSlot(IndexForHash(hashfn_(element)))] = std::move(element);
	}
	allocfn_.destroy(allocfn_.address(element));
	}
	allocfn_.deallocate(old_data, old_num_buckets);
	}
	ALWAYS_INLINE size_t FirstAvailableSlot(size_t index) const {
	while (!emptyfn_.IsEmpty(data_[index])) {
	index = NextIndex(index);
	}
	return index;
	}

	Alloc allocfn_; // Allocator function.
	HashFn hashfn_; // Hashing function.
	EmptyFn emptyfn_; // IsEmpty/SetEmpty function.
	Pred pred_; // Equals function.
	size_t num_elements_; // Number of inserted elements.
	size_t num_buckets_; // Number of hash table buckets.
	size_t elements_until_expand_; // Maxmimum number of elements until we expand the table.
	T* data_; // Backing storage.
	double min_load_factor_;
	double max_load_factor_;

	friend class Iterator;
	};

	} // namespace art

	#endif // ART_RUNTIME_BASE_HASH_SET_H_