v8/src/hashmap.h

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// Copyright 2012 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#ifndef V8_HASHMAP_H_
#define V8_HASHMAP_H_
#include "allocation.h"
#include "checks.h"
#include "utils.h"
namespace v8 {
namespace internal {
template<class AllocationPolicy>
class TemplateHashMapImpl {
public:
typedef bool (*MatchFun) (void* key1, void* key2);
// initial_capacity is the size of the initial hash map;
// it must be a power of 2 (and thus must not be 0).
TemplateHashMapImpl(MatchFun match, uint32_t initial_capacity = 8);
~TemplateHashMapImpl();
// HashMap entries are (key, value, hash) triplets.
// Some clients may not need to use the value slot
// (e.g. implementers of sets, where the key is the value).
struct Entry {
void* key;
void* value;
uint32_t hash; // the full hash value for key
};
// If an entry with matching key is found, Lookup()
// returns that entry. If no matching entry is found,
// but insert is set, a new entry is inserted with
// corresponding key, key hash, and NULL value.
// Otherwise, NULL is returned.
Entry* Lookup(void* key, uint32_t hash, bool insert);
// Removes the entry with matching key.
void Remove(void* key, uint32_t hash);
// Empties the hash map (occupancy() == 0).
void Clear();
// The number of (non-empty) entries in the table.
uint32_t occupancy() const { return occupancy_; }
// The capacity of the table. The implementation
// makes sure that occupancy is at most 80% of
// the table capacity.
uint32_t capacity() const { return capacity_; }
// Iteration
//
// for (Entry* p = map.Start(); p != NULL; p = map.Next(p)) {
// ...
// }
//
// If entries are inserted during iteration, the effect of
// calling Next() is undefined.
Entry* Start() const;
Entry* Next(Entry* p) const;
private:
MatchFun match_;
Entry* map_;
uint32_t capacity_;
uint32_t occupancy_;
Entry* map_end() const { return map_ + capacity_; }
Entry* Probe(void* key, uint32_t hash);
void Initialize(uint32_t capacity);
void Resize();
};
typedef TemplateHashMapImpl<FreeStoreAllocationPolicy> HashMap;
template<class P>
TemplateHashMapImpl<P>::TemplateHashMapImpl(MatchFun match,
uint32_t initial_capacity) {
match_ = match;
Initialize(initial_capacity);
}
template<class P>
TemplateHashMapImpl<P>::~TemplateHashMapImpl() {
P::Delete(map_);
}
template<class P>
typename TemplateHashMapImpl<P>::Entry* TemplateHashMapImpl<P>::Lookup(
void* key, uint32_t hash, bool insert) {
// Find a matching entry.
Entry* p = Probe(key, hash);
if (p->key != NULL) {
return p;
}
// No entry found; insert one if necessary.
if (insert) {
p->key = key;
p->value = NULL;
p->hash = hash;
occupancy_++;
// Grow the map if we reached >= 80% occupancy.
if (occupancy_ + occupancy_/4 >= capacity_) {
Resize();
p = Probe(key, hash);
}
return p;
}
// No entry found and none inserted.
return NULL;
}
template<class P>
void TemplateHashMapImpl<P>::Remove(void* key, uint32_t hash) {
// Lookup the entry for the key to remove.
Entry* p = Probe(key, hash);
if (p->key == NULL) {
// Key not found nothing to remove.
return;
}
// To remove an entry we need to ensure that it does not create an empty
// entry that will cause the search for another entry to stop too soon. If all
// the entries between the entry to remove and the next empty slot have their
// initial position inside this interval, clearing the entry to remove will
// not break the search. If, while searching for the next empty entry, an
// entry is encountered which does not have its initial position between the
// entry to remove and the position looked at, then this entry can be moved to
// the place of the entry to remove without breaking the search for it. The
// entry made vacant by this move is now the entry to remove and the process
// starts over.
// Algorithm from http://en.wikipedia.org/wiki/Open_addressing.
// This guarantees loop termination as there is at least one empty entry so
// eventually the removed entry will have an empty entry after it.
ASSERT(occupancy_ < capacity_);
// p is the candidate entry to clear. q is used to scan forwards.
Entry* q = p; // Start at the entry to remove.
while (true) {
// Move q to the next entry.
q = q + 1;
if (q == map_end()) {
q = map_;
}
// All entries between p and q have their initial position between p and q
// and the entry p can be cleared without breaking the search for these
// entries.
if (q->key == NULL) {
break;
}
// Find the initial position for the entry at position q.
Entry* r = map_ + (q->hash & (capacity_ - 1));
// If the entry at position q has its initial position outside the range
// between p and q it can be moved forward to position p and will still be
// found. There is now a new candidate entry for clearing.
if ((q > p && (r <= p || r > q)) ||
(q < p && (r <= p && r > q))) {
*p = *q;
p = q;
}
}
// Clear the entry which is allowed to en emptied.
p->key = NULL;
occupancy_--;
}
template<class P>
void TemplateHashMapImpl<P>::Clear() {
// Mark all entries as empty.
const Entry* end = map_end();
for (Entry* p = map_; p < end; p++) {
p->key = NULL;
}
occupancy_ = 0;
}
template<class P>
typename TemplateHashMapImpl<P>::Entry* TemplateHashMapImpl<P>::Start() const {
return Next(map_ - 1);
}
template<class P>
typename TemplateHashMapImpl<P>::Entry* TemplateHashMapImpl<P>::Next(Entry* p)
const {
const Entry* end = map_end();
ASSERT(map_ - 1 <= p && p < end);
for (p++; p < end; p++) {
if (p->key != NULL) {
return p;
}
}
return NULL;
}
template<class P>
typename TemplateHashMapImpl<P>::Entry* TemplateHashMapImpl<P>::Probe(void* key,
uint32_t hash) {
ASSERT(key != NULL);
ASSERT(IsPowerOf2(capacity_));
Entry* p = map_ + (hash & (capacity_ - 1));
const Entry* end = map_end();
ASSERT(map_ <= p && p < end);
ASSERT(occupancy_ < capacity_); // Guarantees loop termination.
while (p->key != NULL && (hash != p->hash || !match_(key, p->key))) {
p++;
if (p >= end) {
p = map_;
}
}
return p;
}
template<class P>
void TemplateHashMapImpl<P>::Initialize(uint32_t capacity) {
ASSERT(IsPowerOf2(capacity));
map_ = reinterpret_cast<Entry*>(P::New(capacity * sizeof(Entry)));
if (map_ == NULL) {
v8::internal::FatalProcessOutOfMemory("HashMap::Initialize");
return;
}
capacity_ = capacity;
Clear();
}
template<class P>
void TemplateHashMapImpl<P>::Resize() {
Entry* map = map_;
uint32_t n = occupancy_;
// Allocate larger map.
Initialize(capacity_ * 2);
// Rehash all current entries.
for (Entry* p = map; n > 0; p++) {
if (p->key != NULL) {
Lookup(p->key, p->hash, true)->value = p->value;
n--;
}
}
// Delete old map.
P::Delete(map);
}
// A hash map for pointer keys and values with an STL-like interface.
template<class Key, class Value, class AllocationPolicy>
class TemplateHashMap: private TemplateHashMapImpl<AllocationPolicy> {
public:
STATIC_ASSERT(sizeof(Key*) == sizeof(void*)); // NOLINT
STATIC_ASSERT(sizeof(Value*) == sizeof(void*)); // NOLINT
struct value_type {
Key* first;
Value* second;
};
class Iterator {
public:
Iterator& operator++() {
entry_ = map_->Next(entry_);
return *this;
}
value_type* operator->() { return reinterpret_cast<value_type*>(entry_); }
bool operator!=(const Iterator& other) { return entry_ != other.entry_; }
private:
Iterator(const TemplateHashMapImpl<AllocationPolicy>* map,
typename TemplateHashMapImpl<AllocationPolicy>::Entry* entry) :
map_(map), entry_(entry) { }
const TemplateHashMapImpl<AllocationPolicy>* map_;
typename TemplateHashMapImpl<AllocationPolicy>::Entry* entry_;
friend class TemplateHashMap;
};
TemplateHashMap(
typename TemplateHashMapImpl<AllocationPolicy>::MatchFun match)
: TemplateHashMapImpl<AllocationPolicy>(match) { }
Iterator begin() const { return Iterator(this, this->Start()); }
Iterator end() const { return Iterator(this, NULL); }
Iterator find(Key* key, bool insert = false) {
return Iterator(this, Lookup(key, key->Hash(), insert));
}
};
} } // namespace v8::internal
#endif // V8_HASHMAP_H_