v8/src/hashmap.cc

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// Copyright 2008 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.
#include "v8.h"
#include "hashmap.h"
namespace v8 {
namespace internal {
Allocator HashMap::DefaultAllocator;
HashMap::HashMap() {
allocator_ = NULL;
match_ = NULL;
}
HashMap::HashMap(MatchFun match,
Allocator* allocator,
uint32_t initial_capacity) {
allocator_ = allocator;
match_ = match;
Initialize(initial_capacity);
}
HashMap::~HashMap() {
if (allocator_) {
allocator_->Delete(map_);
}
}
HashMap::Entry* HashMap::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;
}
void HashMap::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_--;
}
void HashMap::Clear() {
// Mark all entries as empty.
const Entry* end = map_end();
for (Entry* p = map_; p < end; p++) {
p->key = NULL;
}
occupancy_ = 0;
}
HashMap::Entry* HashMap::Start() const {
return Next(map_ - 1);
}
HashMap::Entry* HashMap::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;
}
HashMap::Entry* HashMap::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;
}
void HashMap::Initialize(uint32_t capacity) {
ASSERT(IsPowerOf2(capacity));
map_ = reinterpret_cast<Entry*>(allocator_->New(capacity * sizeof(Entry)));
if (map_ == NULL) {
V8::FatalProcessOutOfMemory("HashMap::Initialize");
return;
}
capacity_ = capacity;
Clear();
}
void HashMap::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.
allocator_->Delete(map);
}
} } // namespace v8::internal