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 "src/allocation.h"
9 #include "src/base/bits.h"
10 #include "src/base/logging.h"
11 #include "src/utils.h"
16 template<class AllocationPolicy>
17 class TemplateHashMapImpl {
19 typedef bool (*MatchFun) (void* key1, void* key2);
21 // The default capacity. This is used by the call sites which want
22 // to pass in a non-default AllocationPolicy but want to use the
23 // default value of capacity specified by the implementation.
24 static const uint32_t kDefaultHashMapCapacity = 8;
26 // initial_capacity is the size of the initial hash map;
27 // it must be a power of 2 (and thus must not be 0).
28 TemplateHashMapImpl(MatchFun match,
29 uint32_t capacity = kDefaultHashMapCapacity,
30 AllocationPolicy allocator = AllocationPolicy());
32 ~TemplateHashMapImpl();
34 // HashMap entries are (key, value, hash) triplets.
35 // Some clients may not need to use the value slot
36 // (e.g. implementers of sets, where the key is the value).
40 uint32_t hash; // The full hash value for key
41 int order; // If you never remove entries this is the insertion order.
44 // If an entry with matching key is found, Lookup()
45 // returns that entry. If no matching entry is found,
46 // but insert is set, a new entry is inserted with
47 // corresponding key, key hash, and NULL value.
48 // Otherwise, NULL is returned.
49 Entry* Lookup(void* key, uint32_t hash, bool insert,
50 AllocationPolicy allocator = AllocationPolicy());
52 // Removes the entry with matching key.
53 // It returns the value of the deleted entry
54 // or null if there is no value for such key.
55 void* Remove(void* key, uint32_t hash);
57 // Empties the hash map (occupancy() == 0).
60 // The number of (non-empty) entries in the table.
61 uint32_t occupancy() const { return occupancy_; }
63 // The capacity of the table. The implementation
64 // makes sure that occupancy is at most 80% of
65 // the table capacity.
66 uint32_t capacity() const { return capacity_; }
70 // for (Entry* p = map.Start(); p != NULL; p = map.Next(p)) {
74 // If entries are inserted during iteration, the effect of
75 // calling Next() is undefined.
77 Entry* Next(Entry* p) const;
79 // Some match functions defined for convenience.
80 static bool PointersMatch(void* key1, void* key2) {
90 Entry* map_end() const { return map_ + capacity_; }
91 Entry* Probe(void* key, uint32_t hash);
92 void Initialize(uint32_t capacity, AllocationPolicy allocator);
93 void Resize(AllocationPolicy allocator);
96 typedef TemplateHashMapImpl<FreeStoreAllocationPolicy> HashMap;
98 template<class AllocationPolicy>
99 TemplateHashMapImpl<AllocationPolicy>::TemplateHashMapImpl(
100 MatchFun match, uint32_t initial_capacity, AllocationPolicy allocator) {
102 Initialize(initial_capacity, allocator);
106 template<class AllocationPolicy>
107 TemplateHashMapImpl<AllocationPolicy>::~TemplateHashMapImpl() {
108 AllocationPolicy::Delete(map_);
112 template<class AllocationPolicy>
113 typename TemplateHashMapImpl<AllocationPolicy>::Entry*
114 TemplateHashMapImpl<AllocationPolicy>::Lookup(
115 void* key, uint32_t hash, bool insert, AllocationPolicy allocator) {
116 // Find a matching entry.
117 Entry* p = Probe(key, hash);
118 if (p->key != NULL) {
122 // No entry found; insert one if necessary.
127 p->order = occupancy_;
130 // Grow the map if we reached >= 80% occupancy.
131 if (occupancy_ + occupancy_/4 >= capacity_) {
133 p = Probe(key, hash);
139 // No entry found and none inserted.
144 template<class AllocationPolicy>
145 void* TemplateHashMapImpl<AllocationPolicy>::Remove(void* key, uint32_t hash) {
146 // Lookup the entry for the key to remove.
147 Entry* p = Probe(key, hash);
148 if (p->key == NULL) {
149 // Key not found nothing to remove.
153 void* value = p->value;
154 // To remove an entry we need to ensure that it does not create an empty
155 // entry that will cause the search for another entry to stop too soon. If all
156 // the entries between the entry to remove and the next empty slot have their
157 // initial position inside this interval, clearing the entry to remove will
158 // not break the search. If, while searching for the next empty entry, an
159 // entry is encountered which does not have its initial position between the
160 // entry to remove and the position looked at, then this entry can be moved to
161 // the place of the entry to remove without breaking the search for it. The
162 // entry made vacant by this move is now the entry to remove and the process
164 // Algorithm from http://en.wikipedia.org/wiki/Open_addressing.
166 // This guarantees loop termination as there is at least one empty entry so
167 // eventually the removed entry will have an empty entry after it.
168 DCHECK(occupancy_ < capacity_);
170 // p is the candidate entry to clear. q is used to scan forwards.
171 Entry* q = p; // Start at the entry to remove.
173 // Move q to the next entry.
175 if (q == map_end()) {
179 // All entries between p and q have their initial position between p and q
180 // and the entry p can be cleared without breaking the search for these
182 if (q->key == NULL) {
186 // Find the initial position for the entry at position q.
187 Entry* r = map_ + (q->hash & (capacity_ - 1));
189 // If the entry at position q has its initial position outside the range
190 // between p and q it can be moved forward to position p and will still be
191 // found. There is now a new candidate entry for clearing.
192 if ((q > p && (r <= p || r > q)) ||
193 (q < p && (r <= p && r > q))) {
199 // Clear the entry which is allowed to en emptied.
206 template<class AllocationPolicy>
207 void TemplateHashMapImpl<AllocationPolicy>::Clear() {
208 // Mark all entries as empty.
209 const Entry* end = map_end();
210 for (Entry* p = map_; p < end; p++) {
217 template<class AllocationPolicy>
218 typename TemplateHashMapImpl<AllocationPolicy>::Entry*
219 TemplateHashMapImpl<AllocationPolicy>::Start() const {
220 return Next(map_ - 1);
224 template<class AllocationPolicy>
225 typename TemplateHashMapImpl<AllocationPolicy>::Entry*
226 TemplateHashMapImpl<AllocationPolicy>::Next(Entry* p) const {
227 const Entry* end = map_end();
228 DCHECK(map_ - 1 <= p && p < end);
229 for (p++; p < end; p++) {
230 if (p->key != NULL) {
238 template<class AllocationPolicy>
239 typename TemplateHashMapImpl<AllocationPolicy>::Entry*
240 TemplateHashMapImpl<AllocationPolicy>::Probe(void* key, uint32_t hash) {
243 DCHECK(base::bits::IsPowerOfTwo32(capacity_));
244 Entry* p = map_ + (hash & (capacity_ - 1));
245 const Entry* end = map_end();
246 DCHECK(map_ <= p && p < end);
248 DCHECK(occupancy_ < capacity_); // Guarantees loop termination.
249 while (p->key != NULL && (hash != p->hash || !match_(key, p->key))) {
260 template<class AllocationPolicy>
261 void TemplateHashMapImpl<AllocationPolicy>::Initialize(
262 uint32_t capacity, AllocationPolicy allocator) {
263 DCHECK(base::bits::IsPowerOfTwo32(capacity));
264 map_ = reinterpret_cast<Entry*>(allocator.New(capacity * sizeof(Entry)));
266 v8::internal::FatalProcessOutOfMemory("HashMap::Initialize");
269 capacity_ = capacity;
274 template<class AllocationPolicy>
275 void TemplateHashMapImpl<AllocationPolicy>::Resize(AllocationPolicy allocator) {
277 uint32_t n = occupancy_;
279 // Allocate larger map.
280 Initialize(capacity_ * 2, allocator);
282 // Rehash all current entries.
283 for (Entry* p = map; n > 0; p++) {
284 if (p->key != NULL) {
285 Entry* entry = Lookup(p->key, p->hash, true, allocator);
286 entry->value = p->value;
287 entry->order = p->order;
293 AllocationPolicy::Delete(map);
297 // A hash map for pointer keys and values with an STL-like interface.
298 template<class Key, class Value, class AllocationPolicy>
299 class TemplateHashMap: private TemplateHashMapImpl<AllocationPolicy> {
301 STATIC_ASSERT(sizeof(Key*) == sizeof(void*)); // NOLINT
302 STATIC_ASSERT(sizeof(Value*) == sizeof(void*)); // NOLINT
310 Iterator& operator++() {
311 entry_ = map_->Next(entry_);
315 value_type* operator->() { return reinterpret_cast<value_type*>(entry_); }
316 bool operator!=(const Iterator& other) { return entry_ != other.entry_; }
319 Iterator(const TemplateHashMapImpl<AllocationPolicy>* map,
320 typename TemplateHashMapImpl<AllocationPolicy>::Entry* entry) :
321 map_(map), entry_(entry) { }
323 const TemplateHashMapImpl<AllocationPolicy>* map_;
324 typename TemplateHashMapImpl<AllocationPolicy>::Entry* entry_;
326 friend class TemplateHashMap;
330 typename TemplateHashMapImpl<AllocationPolicy>::MatchFun match,
331 AllocationPolicy allocator = AllocationPolicy())
332 : TemplateHashMapImpl<AllocationPolicy>(
334 TemplateHashMapImpl<AllocationPolicy>::kDefaultHashMapCapacity,
337 Iterator begin() const { return Iterator(this, this->Start()); }
338 Iterator end() const { return Iterator(this, NULL); }
339 Iterator find(Key* key, bool insert = false,
340 AllocationPolicy allocator = AllocationPolicy()) {
341 return Iterator(this, this->Lookup(key, key->Hash(), insert, allocator));
345 } } // namespace v8::internal
347 #endif // V8_HASHMAP_H_