1 // Copyright 2012 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
8 #include "allocation.h"
15 template<class AllocationPolicy>
16 class TemplateHashMapImpl {
18 typedef bool (*MatchFun) (void* key1, void* key2);
20 // The default capacity. This is used by the call sites which want
21 // to pass in a non-default AllocationPolicy but want to use the
22 // default value of capacity specified by the implementation.
23 static const uint32_t kDefaultHashMapCapacity = 8;
25 // initial_capacity is the size of the initial hash map;
26 // it must be a power of 2 (and thus must not be 0).
27 TemplateHashMapImpl(MatchFun match,
28 uint32_t capacity = kDefaultHashMapCapacity,
29 AllocationPolicy allocator = AllocationPolicy());
31 ~TemplateHashMapImpl();
33 // HashMap entries are (key, value, hash) triplets.
34 // Some clients may not need to use the value slot
35 // (e.g. implementers of sets, where the key is the value).
39 uint32_t hash; // The full hash value for key
40 int order; // If you never remove entries this is the insertion order.
43 // If an entry with matching key is found, Lookup()
44 // returns that entry. If no matching entry is found,
45 // but insert is set, a new entry is inserted with
46 // corresponding key, key hash, and NULL value.
47 // Otherwise, NULL is returned.
48 Entry* Lookup(void* key, uint32_t hash, bool insert,
49 AllocationPolicy allocator = AllocationPolicy());
51 // Removes the entry with matching key.
52 // It returns the value of the deleted entry
53 // or null if there is no value for such key.
54 void* Remove(void* key, uint32_t hash);
56 // Empties the hash map (occupancy() == 0).
59 // The number of (non-empty) entries in the table.
60 uint32_t occupancy() const { return occupancy_; }
62 // The capacity of the table. The implementation
63 // makes sure that occupancy is at most 80% of
64 // the table capacity.
65 uint32_t capacity() const { return capacity_; }
69 // for (Entry* p = map.Start(); p != NULL; p = map.Next(p)) {
73 // If entries are inserted during iteration, the effect of
74 // calling Next() is undefined.
76 Entry* Next(Entry* p) const;
78 // Some match functions defined for convenience.
79 static bool PointersMatch(void* key1, void* key2) {
89 Entry* map_end() const { return map_ + capacity_; }
90 Entry* Probe(void* key, uint32_t hash);
91 void Initialize(uint32_t capacity, AllocationPolicy allocator);
92 void Resize(AllocationPolicy allocator);
95 typedef TemplateHashMapImpl<FreeStoreAllocationPolicy> HashMap;
97 template<class AllocationPolicy>
98 TemplateHashMapImpl<AllocationPolicy>::TemplateHashMapImpl(
99 MatchFun match, uint32_t initial_capacity, AllocationPolicy allocator) {
101 Initialize(initial_capacity, allocator);
105 template<class AllocationPolicy>
106 TemplateHashMapImpl<AllocationPolicy>::~TemplateHashMapImpl() {
107 AllocationPolicy::Delete(map_);
111 template<class AllocationPolicy>
112 typename TemplateHashMapImpl<AllocationPolicy>::Entry*
113 TemplateHashMapImpl<AllocationPolicy>::Lookup(
114 void* key, uint32_t hash, bool insert, AllocationPolicy allocator) {
115 // Find a matching entry.
116 Entry* p = Probe(key, hash);
117 if (p->key != NULL) {
121 // No entry found; insert one if necessary.
126 p->order = occupancy_;
129 // Grow the map if we reached >= 80% occupancy.
130 if (occupancy_ + occupancy_/4 >= capacity_) {
132 p = Probe(key, hash);
138 // No entry found and none inserted.
143 template<class AllocationPolicy>
144 void* TemplateHashMapImpl<AllocationPolicy>::Remove(void* key, uint32_t hash) {
145 // Lookup the entry for the key to remove.
146 Entry* p = Probe(key, hash);
147 if (p->key == NULL) {
148 // Key not found nothing to remove.
152 void* value = p->value;
153 // To remove an entry we need to ensure that it does not create an empty
154 // entry that will cause the search for another entry to stop too soon. If all
155 // the entries between the entry to remove and the next empty slot have their
156 // initial position inside this interval, clearing the entry to remove will
157 // not break the search. If, while searching for the next empty entry, an
158 // entry is encountered which does not have its initial position between the
159 // entry to remove and the position looked at, then this entry can be moved to
160 // the place of the entry to remove without breaking the search for it. The
161 // entry made vacant by this move is now the entry to remove and the process
163 // Algorithm from http://en.wikipedia.org/wiki/Open_addressing.
165 // This guarantees loop termination as there is at least one empty entry so
166 // eventually the removed entry will have an empty entry after it.
167 ASSERT(occupancy_ < capacity_);
169 // p is the candidate entry to clear. q is used to scan forwards.
170 Entry* q = p; // Start at the entry to remove.
172 // Move q to the next entry.
174 if (q == map_end()) {
178 // All entries between p and q have their initial position between p and q
179 // and the entry p can be cleared without breaking the search for these
181 if (q->key == NULL) {
185 // Find the initial position for the entry at position q.
186 Entry* r = map_ + (q->hash & (capacity_ - 1));
188 // If the entry at position q has its initial position outside the range
189 // between p and q it can be moved forward to position p and will still be
190 // found. There is now a new candidate entry for clearing.
191 if ((q > p && (r <= p || r > q)) ||
192 (q < p && (r <= p && r > q))) {
198 // Clear the entry which is allowed to en emptied.
205 template<class AllocationPolicy>
206 void TemplateHashMapImpl<AllocationPolicy>::Clear() {
207 // Mark all entries as empty.
208 const Entry* end = map_end();
209 for (Entry* p = map_; p < end; p++) {
216 template<class AllocationPolicy>
217 typename TemplateHashMapImpl<AllocationPolicy>::Entry*
218 TemplateHashMapImpl<AllocationPolicy>::Start() const {
219 return Next(map_ - 1);
223 template<class AllocationPolicy>
224 typename TemplateHashMapImpl<AllocationPolicy>::Entry*
225 TemplateHashMapImpl<AllocationPolicy>::Next(Entry* p) const {
226 const Entry* end = map_end();
227 ASSERT(map_ - 1 <= p && p < end);
228 for (p++; p < end; p++) {
229 if (p->key != NULL) {
237 template<class AllocationPolicy>
238 typename TemplateHashMapImpl<AllocationPolicy>::Entry*
239 TemplateHashMapImpl<AllocationPolicy>::Probe(void* key, uint32_t hash) {
242 ASSERT(IsPowerOf2(capacity_));
243 Entry* p = map_ + (hash & (capacity_ - 1));
244 const Entry* end = map_end();
245 ASSERT(map_ <= p && p < end);
247 ASSERT(occupancy_ < capacity_); // Guarantees loop termination.
248 while (p->key != NULL && (hash != p->hash || !match_(key, p->key))) {
259 template<class AllocationPolicy>
260 void TemplateHashMapImpl<AllocationPolicy>::Initialize(
261 uint32_t capacity, AllocationPolicy allocator) {
262 ASSERT(IsPowerOf2(capacity));
263 map_ = reinterpret_cast<Entry*>(allocator.New(capacity * sizeof(Entry)));
265 v8::internal::FatalProcessOutOfMemory("HashMap::Initialize");
268 capacity_ = capacity;
273 template<class AllocationPolicy>
274 void TemplateHashMapImpl<AllocationPolicy>::Resize(AllocationPolicy allocator) {
276 uint32_t n = occupancy_;
278 // Allocate larger map.
279 Initialize(capacity_ * 2, allocator);
281 // Rehash all current entries.
282 for (Entry* p = map; n > 0; p++) {
283 if (p->key != NULL) {
284 Entry* entry = Lookup(p->key, p->hash, true, allocator);
285 entry->value = p->value;
286 entry->order = p->order;
292 AllocationPolicy::Delete(map);
296 // A hash map for pointer keys and values with an STL-like interface.
297 template<class Key, class Value, class AllocationPolicy>
298 class TemplateHashMap: private TemplateHashMapImpl<AllocationPolicy> {
300 STATIC_ASSERT(sizeof(Key*) == sizeof(void*)); // NOLINT
301 STATIC_ASSERT(sizeof(Value*) == sizeof(void*)); // NOLINT
309 Iterator& operator++() {
310 entry_ = map_->Next(entry_);
314 value_type* operator->() { return reinterpret_cast<value_type*>(entry_); }
315 bool operator!=(const Iterator& other) { return entry_ != other.entry_; }
318 Iterator(const TemplateHashMapImpl<AllocationPolicy>* map,
319 typename TemplateHashMapImpl<AllocationPolicy>::Entry* entry) :
320 map_(map), entry_(entry) { }
322 const TemplateHashMapImpl<AllocationPolicy>* map_;
323 typename TemplateHashMapImpl<AllocationPolicy>::Entry* entry_;
325 friend class TemplateHashMap;
329 typename TemplateHashMapImpl<AllocationPolicy>::MatchFun match,
330 AllocationPolicy allocator = AllocationPolicy())
331 : TemplateHashMapImpl<AllocationPolicy>(
333 TemplateHashMapImpl<AllocationPolicy>::kDefaultHashMapCapacity,
336 Iterator begin() const { return Iterator(this, this->Start()); }
337 Iterator end() const { return Iterator(this, NULL); }
338 Iterator find(Key* key, bool insert = false,
339 AllocationPolicy allocator = AllocationPolicy()) {
340 return Iterator(this, this->Lookup(key, key->Hash(), insert, allocator));
344 } } // namespace v8::internal
346 #endif // V8_HASHMAP_H_