runtime/lib/compact_hash.dart - sdk/ - Git at Google

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 // part of "collection_patch.dart";

 // Hash table with open addressing that separates the index from keys/values.

 // This function takes care of rehashing of the linked hashmaps in [objects]. We
 // do this eagerly after snapshot deserialization.
 @pragma("vm:entry-point")
 void _rehashObjects(List objects) {
   final int length = objects.length;
   for (int i = 0; i < length; ++i) {
     objects[i]._regenerateIndex();
   }
 }

 abstract class _HashFieldBase {
   // Each occupied entry in _index is a fixed-size integer that encodes a pair:
   //   [ hash pattern for key | index of entry in _data ]
   // The hash pattern is based on hashCode, but is guaranteed to be non-zero.
   // The length of _index is always a power of two, and there is always at
   // least one unoccupied entry.
   // NOTE: When maps are deserialized, their _index and _hashMask is regenerated
   // eagerly by _regenerateIndex.
   Uint32List _index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);

   // Cached in-place mask for the hash pattern component.
   int _hashMask = _HashBase._indexSizeToHashMask(_HashBase._INITIAL_INDEX_SIZE);

   // Fixed-length list of keys (set) or key/value at even/odd indices (map).
   List _data;

   // Length of _data that is used (i.e., keys + values for a map).
   int _usedData = 0;

   // Number of deleted keys.
   int _deletedKeys = 0;

   // Note: All fields are initialized in a single constructor so that the VM
   // recognizes they cannot hold null values. This makes a big (20%) performance
   // difference on some operations.
   _HashFieldBase(int dataSize) : this._data = new List(dataSize);
 }

 // Base class for VM-internal classes; keep in sync with _HashFieldBase.
 abstract class _HashVMBase {
   @pragma("vm:exact-result-type", "dart:typed_data#_Uint32List")
   Uint32List get _index native "LinkedHashMap_getIndex";
   void set _index(Uint32List value) native "LinkedHashMap_setIndex";

   @pragma("vm:exact-result-type", "dart:core#_Smi")
   int get _hashMask native "LinkedHashMap_getHashMask";
   void set _hashMask(int value) native "LinkedHashMap_setHashMask";

   @pragma("vm:exact-result-type", "dart:core#_List")
   List get _data native "LinkedHashMap_getData";
   void set _data(List value) native "LinkedHashMap_setData";

   @pragma("vm:exact-result-type", "dart:core#_Smi")
   int get _usedData native "LinkedHashMap_getUsedData";
   void set _usedData(int value) native "LinkedHashMap_setUsedData";

   @pragma("vm:exact-result-type", "dart:core#_Smi")
   int get _deletedKeys native "LinkedHashMap_getDeletedKeys";
   void set _deletedKeys(int value) native "LinkedHashMap_setDeletedKeys";
 }

 // This mixin can be applied to _HashFieldBase or _HashVMBase (for
 // normal and VM-internalized classes, respectiveley), which provide the
 // actual fields/accessors that this mixin assumes.
 // TODO(koda): Consider moving field comments to _HashFieldBase.
 abstract class _HashBase implements _HashVMBase {
   // The number of bits used for each component is determined by table size.
   // The length of _index is twice the number of entries in _data, and both
   // are doubled when _data is full. Thus, _index will have a max load factor
   // of 1/2, which enables one more bit to be used for the hash.
   // TODO(koda): Consider growing _data by factor sqrt(2), twice as often.
   static const int _INITIAL_INDEX_BITS = 3;
   static const int _INITIAL_INDEX_SIZE = 1 << (_INITIAL_INDEX_BITS + 1);

   // Unused and deleted entries are marked by 0 and 1, respectively.
   static const int _UNUSED_PAIR = 0;
   static const int _DELETED_PAIR = 1;

   // On 32-bit, the top bits are wasted to avoid Mint allocation.
   // TODO(koda): Reclaim the bits by making the compiler treat hash patterns
   // as unsigned words.
   static int _indexSizeToHashMask(int indexSize) {
     int indexBits = indexSize.bitLength - 2;
     return internal.is64Bit
         ? (1 << (32 - indexBits)) - 1
         : (1 << (30 - indexBits)) - 1;
   }

   static int _hashPattern(int fullHash, int hashMask, int size) {
     final int maskedHash = fullHash & hashMask;
     // TODO(koda): Consider keeping bit length and use left shift.
     return (maskedHash == 0) ? (size >> 1) : maskedHash * (size >> 1);
   }

   // Linear probing.
   static int _firstProbe(int fullHash, int sizeMask) {
     final int i = fullHash & sizeMask;
     // Light, fast shuffle to mitigate bad hashCode (e.g., sequential).
     return ((i << 1) + i) & sizeMask;
   }

   static int _nextProbe(int i, int sizeMask) => (i + 1) & sizeMask;

   // A self-loop is used to mark a deleted key or value.
   static bool _isDeleted(List data, Object keyOrValue) =>
       identical(keyOrValue, data);
   static void _setDeletedAt(List data, int d) {
     data[d] = data;
   }

   // Concurrent modification detection relies on this checksum monotonically
   // increasing between reallocations of _data.
   int get _checkSum => _usedData + _deletedKeys;
   bool _isModifiedSince(List oldData, int oldCheckSum) =>
       !identical(_data, oldData) || (_checkSum != oldCheckSum);

   int get length;
 }

 class _OperatorEqualsAndHashCode {
   int _hashCode(e) => e.hashCode;
   bool _equals(e1, e2) => e1 == e2;
 }

 class _IdenticalAndIdentityHashCode {
   int _hashCode(e) => identityHashCode(e);
   bool _equals(e1, e2) => identical(e1, e2);
 }

 // VM-internalized implementation of a default-constructed LinkedHashMap.
 @pragma("vm:entry-point")
 class _InternalLinkedHashMap<K, V> extends _HashVMBase
     with
         MapMixin<K, V>,
         _LinkedHashMapMixin<K, V>,
         _HashBase,
         _OperatorEqualsAndHashCode
     implements LinkedHashMap<K, V> {
   _InternalLinkedHashMap() {
     _index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);
     _hashMask = _HashBase._indexSizeToHashMask(_HashBase._INITIAL_INDEX_SIZE);
     _data = new List(_HashBase._INITIAL_INDEX_SIZE);
     _usedData = 0;
     _deletedKeys = 0;
   }
 }

 abstract class _LinkedHashMapMixin<K, V> implements _HashBase {
   int _hashCode(e);
   bool _equals(e1, e2);
   int get _checkSum;
   bool _isModifiedSince(List oldData, int oldCheckSum);

   int get length => (_usedData >> 1) - _deletedKeys;
   bool get isEmpty => length == 0;
   bool get isNotEmpty => !isEmpty;

   void _rehash() {
     if ((_deletedKeys << 2) > _usedData) {
       // TODO(koda): Consider shrinking.
       // TODO(koda): Consider in-place compaction and more costly CME check.
       _init(_index.length, _hashMask, _data, _usedData);
     } else {
       // TODO(koda): Support 32->64 bit transition (and adjust _hashMask).
       _init(_index.length << 1, _hashMask >> 1, _data, _usedData);
     }
   }

   void clear() {
     if (!isEmpty) {
       _init(_HashBase._INITIAL_INDEX_SIZE, _hashMask, null, 0);
     }
   }

   // Allocate new _index and _data, and optionally copy existing contents.
   void _init(int size, int hashMask, List oldData, int oldUsed) {
     assert(size & (size - 1) == 0);
     assert(_HashBase._UNUSED_PAIR == 0);
     _index = new Uint32List(size);
     _hashMask = hashMask;
     _data = new List(size);
     _usedData = 0;
     _deletedKeys = 0;
     if (oldData != null) {
       for (int i = 0; i < oldUsed; i += 2) {
         var key = oldData[i];
         if (!_HashBase._isDeleted(oldData, key)) {
           // TODO(koda): While there are enough hash bits, avoid hashCode calls.
           this[key] = oldData[i + 1];
         }
       }
     }
   }

   // This method is called by [_rehashObjects] (see above).
   void _regenerateIndex() {
     _index = new Uint32List(_data.length);
     assert(_hashMask == 0);
     _hashMask = _HashBase._indexSizeToHashMask(_index.length);
     final int tmpUsed = _usedData;
     _usedData = 0;
     for (int i = 0; i < tmpUsed; i += 2) {
       this[_data[i]] = _data[i + 1];
     }
   }

   void _insert(K key, V value, int hashPattern, int i) {
     if (_usedData == _data.length) {
       _rehash();
       this[key] = value;
     } else {
       assert(1 <= hashPattern && hashPattern < (1 << 32));
       final int index = _usedData >> 1;
       assert((index & hashPattern) == 0);
       _index[i] = hashPattern | index;
       _data[_usedData++] = key;
       _data[_usedData++] = value;
     }
   }

   // If key is present, returns the index of the value in _data, else returns
   // the negated insertion point in _index.
   int _findValueOrInsertPoint(K key, int fullHash, int hashPattern, int size) {
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int firstDeleted = -1;
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair == _HashBase._DELETED_PAIR) {
         if (firstDeleted < 0) {
           firstDeleted = i;
         }
       } else {
         final int entry = hashPattern ^ pair;
         if (entry < maxEntries) {
           final int d = entry << 1;
           if (_equals(key, _data[d])) {
             return d + 1;
           }
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return firstDeleted >= 0 ? -firstDeleted : -i;
   }

   void operator []=(K key, V value) {
     final int size = _index.length;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     final int d = _findValueOrInsertPoint(key, fullHash, hashPattern, size);
     if (d > 0) {
       _data[d] = value;
     } else {
       final int i = -d;
       _insert(key, value, hashPattern, i);
     }
   }

   V putIfAbsent(K key, V ifAbsent()) {
     final int size = _index.length;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     final int d = _findValueOrInsertPoint(key, fullHash, hashPattern, size);
     if (d > 0) {
       return _data[d];
     }
     // 'ifAbsent' is allowed to modify the map.
     List oldData = _data;
     int oldCheckSum = _checkSum;
     V value = ifAbsent();
     if (_isModifiedSince(oldData, oldCheckSum)) {
       this[key] = value;
     } else {
       final int i = -d;
       _insert(key, value, hashPattern, i);
     }
     return value;
   }

   V remove(Object key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair != _HashBase._DELETED_PAIR) {
         final int entry = hashPattern ^ pair;
         if (entry < maxEntries) {
           final int d = entry << 1;
           if (_equals(key, _data[d])) {
             _index[i] = _HashBase._DELETED_PAIR;
             _HashBase._setDeletedAt(_data, d);
             V value = _data[d + 1];
             _HashBase._setDeletedAt(_data, d + 1);
             ++_deletedKeys;
             return value;
           }
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return null;
   }

   // If key is absent, return _data (which is never a value).
   Object _getValueOrData(Object key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair != _HashBase._DELETED_PAIR) {
         final int entry = hashPattern ^ pair;
         if (entry < maxEntries) {
           final int d = entry << 1;
           if (_equals(key, _data[d])) {
             return _data[d + 1];
           }
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return _data;
   }

   bool containsKey(Object key) => !identical(_data, _getValueOrData(key));

   V operator [](Object key) {
     var v = _getValueOrData(key);
     return identical(_data, v) ? null : internal.unsafeCast<V>(v);
   }

   bool containsValue(Object value) {
     for (var v in values) {
       // Spec. says this should always use "==", also for identity maps, etc.
       if (v == value) {
         return true;
       }
     }
     return false;
   }

   void forEach(void f(K key, V value)) {
     var ki = keys.iterator;
     var vi = values.iterator;
     while (ki.moveNext()) {
       vi.moveNext();
       f(ki.current, vi.current);
     }
   }

   Iterable<K> get keys =>
       new _CompactIterable<K>(this, _data, _usedData, -2, 2);
   Iterable<V> get values =>
       new _CompactIterable<V>(this, _data, _usedData, -1, 2);
 }

 class _CompactLinkedIdentityHashMap<K, V> extends _HashFieldBase
     with
         MapMixin<K, V>,
         _LinkedHashMapMixin<K, V>,
         _HashBase,
         _IdenticalAndIdentityHashCode
     implements LinkedHashMap<K, V> {
   _CompactLinkedIdentityHashMap() : super(_HashBase._INITIAL_INDEX_SIZE);
 }

 class _CompactLinkedCustomHashMap<K, V> extends _HashFieldBase
     with MapMixin<K, V>, _LinkedHashMapMixin<K, V>, _HashBase
     implements LinkedHashMap<K, V> {
   final _equality;
   final _hasher;
   final _validKey;

   // TODO(koda): Ask gbracha why I cannot have fields _equals/_hashCode.
   int _hashCode(e) => _hasher(e);
   bool _equals(e1, e2) => _equality(e1, e2);

   bool containsKey(Object o) => _validKey(o) ? super.containsKey(o) : false;
   V operator [](Object o) => _validKey(o) ? super[o] : null;
   V remove(Object o) => _validKey(o) ? super.remove(o) : null;

   _CompactLinkedCustomHashMap(this._equality, this._hasher, validKey)
       : _validKey = (validKey != null) ? validKey : new _TypeTest<K>().test,
         super(_HashBase._INITIAL_INDEX_SIZE);
 }

 // Iterates through _data[_offset + _step], _data[_offset + 2*_step], ...
 // and checks for concurrent modification.
 class _CompactIterable<E> extends Iterable<E> {
   final _HashBase _table;
   final List _data;
   final int _len;
   final int _offset;
   final int _step;

   _CompactIterable(
       this._table, this._data, this._len, this._offset, this._step);

   Iterator<E> get iterator =>
       new _CompactIterator<E>(_table, _data, _len, _offset, _step);

   int get length => _table.length;
   bool get isEmpty => length == 0;
   bool get isNotEmpty => !isEmpty;
 }

 class _CompactIterator<E> implements Iterator<E> {
   final _HashBase _table;
   final List _data;
   final int _len;
   int _offset;
   final int _step;
   final int _checkSum;
   E current;

   _CompactIterator(
       _HashBase table, this._data, this._len, this._offset, this._step)
       : _table = table,
         _checkSum = table._checkSum;

   bool moveNext() {
     if (_table._isModifiedSince(_data, _checkSum)) {
       throw new ConcurrentModificationError(_table);
     }
     do {
       _offset += _step;
     } while (_offset < _len && _HashBase._isDeleted(_data, _data[_offset]));
     if (_offset < _len) {
       current = internal.unsafeCast<E>(_data[_offset]);
       return true;
     } else {
       current = null;
       return false;
     }
   }
 }

 // Set implementation, analogous to _CompactLinkedHashMap.
 class _CompactLinkedHashSet<E> extends _HashFieldBase
     with _HashBase, _OperatorEqualsAndHashCode, SetMixin<E>
     implements LinkedHashSet<E> {
   _CompactLinkedHashSet() : super(_HashBase._INITIAL_INDEX_SIZE >> 1) {
     assert(_HashBase._UNUSED_PAIR == 0);
   }

   static Set<R> _newEmpty<R>() => new _CompactLinkedHashSet<R>();

   Set<R> cast<R>() => Set.castFrom<E, R>(this, newSet: _newEmpty);
   int get length => _usedData - _deletedKeys;

   E get first {
     for (int offset = 0; offset < _usedData; offset++) {
       Object current = _data[offset];
       if (!_HashBase._isDeleted(_data, current)) {
         return current;
       }
     }
     throw IterableElementError.noElement();
   }

   E get last {
     for (int offset = _usedData - 1; offset >= 0; offset--) {
       Object current = _data[offset];
       if (!_HashBase._isDeleted(_data, current)) {
         return current;
       }
     }
     throw IterableElementError.noElement();
   }

   void _rehash() {
     if ((_deletedKeys << 1) > _usedData) {
       _init(_index.length, _hashMask, _data, _usedData);
     } else {
       _init(_index.length << 1, _hashMask >> 1, _data, _usedData);
     }
   }

   void clear() {
     if (!isEmpty) {
       _init(_HashBase._INITIAL_INDEX_SIZE, _hashMask, null, 0);
     }
   }

   void _init(int size, int hashMask, List oldData, int oldUsed) {
     _index = new Uint32List(size);
     _hashMask = hashMask;
     _data = new List(size >> 1);
     _usedData = 0;
     _deletedKeys = 0;
     if (oldData != null) {
       for (int i = 0; i < oldUsed; i += 1) {
         var key = oldData[i];
         if (!_HashBase._isDeleted(oldData, key)) {
           add(key);
         }
       }
     }
   }

   bool add(E key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int firstDeleted = -1;
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair == _HashBase._DELETED_PAIR) {
         if (firstDeleted < 0) {
           firstDeleted = i;
         }
       } else {
         final int d = hashPattern ^ pair;
         if (d < maxEntries && _equals(key, _data[d])) {
           return false;
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     if (_usedData == _data.length) {
       _rehash();
       add(key);
     } else {
       final int insertionPoint = (firstDeleted >= 0) ? firstDeleted : i;
       assert(1 <= hashPattern && hashPattern < (1 << 32));
       assert((hashPattern & _usedData) == 0);
       _index[insertionPoint] = hashPattern | _usedData;
       _data[_usedData++] = key;
     }
     return true;
   }

   // If key is absent, return _data (which is never a value).
   Object _getKeyOrData(Object key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair != _HashBase._DELETED_PAIR) {
         final int d = hashPattern ^ pair;
         if (d < maxEntries && _equals(key, _data[d])) {
           return _data[d]; // Note: Must return the existing key.
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return _data;
   }

   E lookup(Object key) {
     var k = _getKeyOrData(key);
     return identical(_data, k) ? null : k;
   }

   bool contains(Object key) => !identical(_data, _getKeyOrData(key));

   bool remove(Object key) {
     final int size = _index.length;
     final int sizeMask = size - 1;
     final int maxEntries = size >> 1;
     final int fullHash = _hashCode(key);
     final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
     int i = _HashBase._firstProbe(fullHash, sizeMask);
     int pair = _index[i];
     while (pair != _HashBase._UNUSED_PAIR) {
       if (pair != _HashBase._DELETED_PAIR) {
         final int d = hashPattern ^ pair;
         if (d < maxEntries && _equals(key, _data[d])) {
           _index[i] = _HashBase._DELETED_PAIR;
           _HashBase._setDeletedAt(_data, d);
           ++_deletedKeys;
           return true;
         }
       }
       i = _HashBase._nextProbe(i, sizeMask);
       pair = _index[i];
     }
     return false;
   }

   Iterator<E> get iterator =>
       new _CompactIterator<E>(this, _data, _usedData, -1, 1);

   // Returns a set of the same type, although this
   // is not required by the spec. (For instance, always using an identity set
   // would be technically correct, albeit surprising.)
   Set<E> toSet() => new _CompactLinkedHashSet<E>()..addAll(this);
 }

 class _CompactLinkedIdentityHashSet<E> extends _CompactLinkedHashSet<E>
     with _IdenticalAndIdentityHashCode {
   Set<E> toSet() => new _CompactLinkedIdentityHashSet<E>()..addAll(this);

   static Set<R> _newEmpty<R>() => new _CompactLinkedIdentityHashSet<R>();

   Set<R> cast<R>() => Set.castFrom<E, R>(this, newSet: _newEmpty);
 }

 class _CompactLinkedCustomHashSet<E> extends _CompactLinkedHashSet<E> {
   final _equality;
   final _hasher;
   final _validKey;

   int _hashCode(e) => _hasher(e);
   bool _equals(e1, e2) => _equality(e1, e2);

   bool contains(Object o) => _validKey(o) ? super.contains(o) : false;
   E lookup(Object o) => _validKey(o) ? super.lookup(o) : null;
   bool remove(Object o) => _validKey(o) ? super.remove(o) : false;

   _CompactLinkedCustomHashSet(this._equality, this._hasher, validKey)
       : _validKey = (validKey != null) ? validKey : new _TypeTest<E>().test;

   Set<R> cast<R>() => Set.castFrom<E, R>(this);
   Set<E> toSet() =>
       new _CompactLinkedCustomHashSet<E>(_equality, _hasher, _validKey)
         ..addAll(this);
 }
	// Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.

	// part of "collection_patch.dart";

	// Hash table with open addressing that separates the index from keys/values.

	// This function takes care of rehashing of the linked hashmaps in [objects]. We
	// do this eagerly after snapshot deserialization.
	@pragma("vm:entry-point")
	void _rehashObjects(List objects) {
	final int length = objects.length;
	for (int i = 0; i < length; ++i) {
	objects[i]._regenerateIndex();
	}
	}

	abstract class _HashFieldBase {
	// Each occupied entry in _index is a fixed-size integer that encodes a pair:
	// [ hash pattern for key \| index of entry in _data ]
	// The hash pattern is based on hashCode, but is guaranteed to be non-zero.
	// The length of _index is always a power of two, and there is always at
	// least one unoccupied entry.
	// NOTE: When maps are deserialized, their _index and _hashMask is regenerated
	// eagerly by _regenerateIndex.
	Uint32List _index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);

	// Cached in-place mask for the hash pattern component.
	int _hashMask = _HashBase._indexSizeToHashMask(_HashBase._INITIAL_INDEX_SIZE);

	// Fixed-length list of keys (set) or key/value at even/odd indices (map).
	List _data;

	// Length of _data that is used (i.e., keys + values for a map).
	int _usedData = 0;

	// Number of deleted keys.
	int _deletedKeys = 0;

	// Note: All fields are initialized in a single constructor so that the VM
	// recognizes they cannot hold null values. This makes a big (20%) performance
	// difference on some operations.
	_HashFieldBase(int dataSize) : this._data = new List(dataSize);
	}

	// Base class for VM-internal classes; keep in sync with _HashFieldBase.
	abstract class _HashVMBase {
	@pragma("vm:exact-result-type", "dart:typed_data#_Uint32List")
	Uint32List get _index native "LinkedHashMap_getIndex";
	void set _index(Uint32List value) native "LinkedHashMap_setIndex";

	@pragma("vm:exact-result-type", "dart:core#_Smi")
	int get _hashMask native "LinkedHashMap_getHashMask";
	void set _hashMask(int value) native "LinkedHashMap_setHashMask";

	@pragma("vm:exact-result-type", "dart:core#_List")
	List get _data native "LinkedHashMap_getData";
	void set _data(List value) native "LinkedHashMap_setData";

	@pragma("vm:exact-result-type", "dart:core#_Smi")
	int get _usedData native "LinkedHashMap_getUsedData";
	void set _usedData(int value) native "LinkedHashMap_setUsedData";

	@pragma("vm:exact-result-type", "dart:core#_Smi")
	int get _deletedKeys native "LinkedHashMap_getDeletedKeys";
	void set _deletedKeys(int value) native "LinkedHashMap_setDeletedKeys";
	}

	// This mixin can be applied to _HashFieldBase or _HashVMBase (for
	// normal and VM-internalized classes, respectiveley), which provide the
	// actual fields/accessors that this mixin assumes.
	// TODO(koda): Consider moving field comments to _HashFieldBase.
	abstract class _HashBase implements _HashVMBase {
	// The number of bits used for each component is determined by table size.
	// The length of _index is twice the number of entries in _data, and both
	// are doubled when _data is full. Thus, _index will have a max load factor
	// of 1/2, which enables one more bit to be used for the hash.
	// TODO(koda): Consider growing _data by factor sqrt(2), twice as often.
	static const int _INITIAL_INDEX_BITS = 3;
	static const int _INITIAL_INDEX_SIZE = 1 << (_INITIAL_INDEX_BITS + 1);

	// Unused and deleted entries are marked by 0 and 1, respectively.
	static const int _UNUSED_PAIR = 0;
	static const int _DELETED_PAIR = 1;

	// On 32-bit, the top bits are wasted to avoid Mint allocation.
	// TODO(koda): Reclaim the bits by making the compiler treat hash patterns
	// as unsigned words.
	static int _indexSizeToHashMask(int indexSize) {
	int indexBits = indexSize.bitLength - 2;
	return internal.is64Bit
	? (1 << (32 - indexBits)) - 1
	: (1 << (30 - indexBits)) - 1;
	}

	static int _hashPattern(int fullHash, int hashMask, int size) {
	final int maskedHash = fullHash & hashMask;
	// TODO(koda): Consider keeping bit length and use left shift.
	return (maskedHash == 0) ? (size >> 1) : maskedHash * (size >> 1);
	}

	// Linear probing.
	static int _firstProbe(int fullHash, int sizeMask) {
	final int i = fullHash & sizeMask;
	// Light, fast shuffle to mitigate bad hashCode (e.g., sequential).
	return ((i << 1) + i) & sizeMask;
	}

	static int _nextProbe(int i, int sizeMask) => (i + 1) & sizeMask;

	// A self-loop is used to mark a deleted key or value.
	static bool _isDeleted(List data, Object keyOrValue) =>
	identical(keyOrValue, data);
	static void _setDeletedAt(List data, int d) {
	data[d] = data;
	}

	// Concurrent modification detection relies on this checksum monotonically
	// increasing between reallocations of _data.
	int get _checkSum => _usedData + _deletedKeys;
	bool _isModifiedSince(List oldData, int oldCheckSum) =>
	!identical(_data, oldData) \|\| (_checkSum != oldCheckSum);

	int get length;
	}

	class _OperatorEqualsAndHashCode {
	int _hashCode(e) => e.hashCode;
	bool _equals(e1, e2) => e1 == e2;
	}

	class _IdenticalAndIdentityHashCode {
	int _hashCode(e) => identityHashCode(e);
	bool _equals(e1, e2) => identical(e1, e2);
	}

	// VM-internalized implementation of a default-constructed LinkedHashMap.
	@pragma("vm:entry-point")
	class _InternalLinkedHashMap<K, V> extends _HashVMBase
	with
	MapMixin<K, V>,
	_LinkedHashMapMixin<K, V>,
	_HashBase,
	_OperatorEqualsAndHashCode
	implements LinkedHashMap<K, V> {
	_InternalLinkedHashMap() {
	_index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);
	_hashMask = _HashBase._indexSizeToHashMask(_HashBase._INITIAL_INDEX_SIZE);
	_data = new List(_HashBase._INITIAL_INDEX_SIZE);
	_usedData = 0;
	_deletedKeys = 0;
	}
	}

	abstract class _LinkedHashMapMixin<K, V> implements _HashBase {
	int _hashCode(e);
	bool _equals(e1, e2);
	int get _checkSum;
	bool _isModifiedSince(List oldData, int oldCheckSum);

	int get length => (_usedData >> 1) - _deletedKeys;
	bool get isEmpty => length == 0;
	bool get isNotEmpty => !isEmpty;

	void _rehash() {
	if ((_deletedKeys << 2) > _usedData) {
	// TODO(koda): Consider shrinking.
	// TODO(koda): Consider in-place compaction and more costly CME check.
	_init(_index.length, _hashMask, _data, _usedData);
	} else {
	// TODO(koda): Support 32->64 bit transition (and adjust _hashMask).
	_init(_index.length << 1, _hashMask >> 1, _data, _usedData);
	}
	}

	void clear() {
	if (!isEmpty) {
	_init(_HashBase._INITIAL_INDEX_SIZE, _hashMask, null, 0);
	}
	}

	// Allocate new _index and _data, and optionally copy existing contents.
	void _init(int size, int hashMask, List oldData, int oldUsed) {
	assert(size & (size - 1) == 0);
	assert(_HashBase._UNUSED_PAIR == 0);
	_index = new Uint32List(size);
	_hashMask = hashMask;
	_data = new List(size);
	_usedData = 0;
	_deletedKeys = 0;
	if (oldData != null) {
	for (int i = 0; i < oldUsed; i += 2) {
	var key = oldData[i];
	if (!_HashBase._isDeleted(oldData, key)) {
	// TODO(koda): While there are enough hash bits, avoid hashCode calls.
	this[key] = oldData[i + 1];
	}
	}
	}
	}

	// This method is called by [_rehashObjects] (see above).
	void _regenerateIndex() {
	_index = new Uint32List(_data.length);
	assert(_hashMask == 0);
	_hashMask = _HashBase._indexSizeToHashMask(_index.length);
	final int tmpUsed = _usedData;
	_usedData = 0;
	for (int i = 0; i < tmpUsed; i += 2) {
	this[_data[i]] = _data[i + 1];
	}
	}

	void _insert(K key, V value, int hashPattern, int i) {
	if (_usedData == _data.length) {
	_rehash();
	this[key] = value;
	} else {
	assert(1 <= hashPattern && hashPattern < (1 << 32));
	final int index = _usedData >> 1;
	assert((index & hashPattern) == 0);
	_index[i] = hashPattern \| index;
	_data[_usedData++] = key;
	_data[_usedData++] = value;
	}
	}

	// If key is present, returns the index of the value in _data, else returns
	// the negated insertion point in _index.
	int _findValueOrInsertPoint(K key, int fullHash, int hashPattern, int size) {
	final int sizeMask = size - 1;
	final int maxEntries = size >> 1;
	int i = _HashBase._firstProbe(fullHash, sizeMask);
	int firstDeleted = -1;
	int pair = _index[i];
	while (pair != _HashBase._UNUSED_PAIR) {
	if (pair == _HashBase._DELETED_PAIR) {
	if (firstDeleted < 0) {
	firstDeleted = i;
	}
	} else {
	final int entry = hashPattern ^ pair;
	if (entry < maxEntries) {
	final int d = entry << 1;
	if (_equals(key, _data[d])) {
	return d + 1;
	}
	}
	}
	i = _HashBase._nextProbe(i, sizeMask);
	pair = _index[i];
	}
	return firstDeleted >= 0 ? -firstDeleted : -i;
	}

	void operator []=(K key, V value) {
	final int size = _index.length;
	final int fullHash = _hashCode(key);
	final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
	final int d = _findValueOrInsertPoint(key, fullHash, hashPattern, size);
	if (d > 0) {
	_data[d] = value;
	} else {
	final int i = -d;
	_insert(key, value, hashPattern, i);
	}
	}

	V putIfAbsent(K key, V ifAbsent()) {
	final int size = _index.length;
	final int fullHash = _hashCode(key);
	final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
	final int d = _findValueOrInsertPoint(key, fullHash, hashPattern, size);
	if (d > 0) {
	return _data[d];
	}
	// 'ifAbsent' is allowed to modify the map.
	List oldData = _data;
	int oldCheckSum = _checkSum;
	V value = ifAbsent();
	if (_isModifiedSince(oldData, oldCheckSum)) {
	this[key] = value;
	} else {
	final int i = -d;
	_insert(key, value, hashPattern, i);
	}
	return value;
	}

	V remove(Object key) {
	final int size = _index.length;
	final int sizeMask = size - 1;
	final int maxEntries = size >> 1;
	final int fullHash = _hashCode(key);
	final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
	int i = _HashBase._firstProbe(fullHash, sizeMask);
	int pair = _index[i];
	while (pair != _HashBase._UNUSED_PAIR) {
	if (pair != _HashBase._DELETED_PAIR) {
	final int entry = hashPattern ^ pair;
	if (entry < maxEntries) {
	final int d = entry << 1;
	if (_equals(key, _data[d])) {
	_index[i] = _HashBase._DELETED_PAIR;
	_HashBase._setDeletedAt(_data, d);
	V value = _data[d + 1];
	_HashBase._setDeletedAt(_data, d + 1);
	++_deletedKeys;
	return value;
	}
	}
	}
	i = _HashBase._nextProbe(i, sizeMask);
	pair = _index[i];
	}
	return null;
	}

	// If key is absent, return _data (which is never a value).
	Object _getValueOrData(Object key) {
	final int size = _index.length;
	final int sizeMask = size - 1;
	final int maxEntries = size >> 1;
	final int fullHash = _hashCode(key);
	final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
	int i = _HashBase._firstProbe(fullHash, sizeMask);
	int pair = _index[i];
	while (pair != _HashBase._UNUSED_PAIR) {
	if (pair != _HashBase._DELETED_PAIR) {
	final int entry = hashPattern ^ pair;
	if (entry < maxEntries) {
	final int d = entry << 1;
	if (_equals(key, _data[d])) {
	return _data[d + 1];
	}
	}
	}
	i = _HashBase._nextProbe(i, sizeMask);
	pair = _index[i];
	}
	return _data;
	}

	bool containsKey(Object key) => !identical(_data, _getValueOrData(key));

	V operator [](Object key) {
	var v = _getValueOrData(key);
	return identical(_data, v) ? null : internal.unsafeCast<V>(v);
	}

	bool containsValue(Object value) {
	for (var v in values) {
	// Spec. says this should always use "==", also for identity maps, etc.
	if (v == value) {
	return true;
	}
	}
	return false;
	}

	void forEach(void f(K key, V value)) {
	var ki = keys.iterator;
	var vi = values.iterator;
	while (ki.moveNext()) {
	vi.moveNext();
	f(ki.current, vi.current);
	}
	}

	Iterable<K> get keys =>
	new _CompactIterable<K>(this, _data, _usedData, -2, 2);
	Iterable<V> get values =>
	new _CompactIterable<V>(this, _data, _usedData, -1, 2);
	}

	class _CompactLinkedIdentityHashMap<K, V> extends _HashFieldBase
	with
	MapMixin<K, V>,
	_LinkedHashMapMixin<K, V>,
	_HashBase,
	_IdenticalAndIdentityHashCode
	implements LinkedHashMap<K, V> {
	_CompactLinkedIdentityHashMap() : super(_HashBase._INITIAL_INDEX_SIZE);
	}

	class _CompactLinkedCustomHashMap<K, V> extends _HashFieldBase
	with MapMixin<K, V>, _LinkedHashMapMixin<K, V>, _HashBase
	implements LinkedHashMap<K, V> {
	final _equality;
	final _hasher;
	final _validKey;

	// TODO(koda): Ask gbracha why I cannot have fields _equals/_hashCode.
	int _hashCode(e) => _hasher(e);
	bool _equals(e1, e2) => _equality(e1, e2);

	bool containsKey(Object o) => _validKey(o) ? super.containsKey(o) : false;
	V operator [](Object o) => _validKey(o) ? super[o] : null;
	V remove(Object o) => _validKey(o) ? super.remove(o) : null;

	_CompactLinkedCustomHashMap(this._equality, this._hasher, validKey)
	: _validKey = (validKey != null) ? validKey : new _TypeTest<K>().test,
	super(_HashBase._INITIAL_INDEX_SIZE);
	}

	// Iterates through _data[_offset + _step], _data[_offset + 2*_step], ...
	// and checks for concurrent modification.
	class _CompactIterable<E> extends Iterable<E> {
	final _HashBase _table;
	final List _data;
	final int _len;
	final int _offset;
	final int _step;

	_CompactIterable(
	this._table, this._data, this._len, this._offset, this._step);

	Iterator<E> get iterator =>
	new _CompactIterator<E>(_table, _data, _len, _offset, _step);

	int get length => _table.length;
	bool get isEmpty => length == 0;
	bool get isNotEmpty => !isEmpty;
	}

	class _CompactIterator<E> implements Iterator<E> {
	final _HashBase _table;
	final List _data;
	final int _len;
	int _offset;
	final int _step;
	final int _checkSum;
	E current;

	_CompactIterator(
	_HashBase table, this._data, this._len, this._offset, this._step)
	: _table = table,
	_checkSum = table._checkSum;

	bool moveNext() {
	if (_table._isModifiedSince(_data, _checkSum)) {
	throw new ConcurrentModificationError(_table);
	}
	do {
	_offset += _step;
	} while (_offset < _len && _HashBase._isDeleted(_data, _data[_offset]));
	if (_offset < _len) {
	current = internal.unsafeCast<E>(_data[_offset]);
	return true;
	} else {
	current = null;
	return false;
	}
	}
	}

	// Set implementation, analogous to _CompactLinkedHashMap.
	class _CompactLinkedHashSet<E> extends _HashFieldBase
	with _HashBase, _OperatorEqualsAndHashCode, SetMixin<E>
	implements LinkedHashSet<E> {
	_CompactLinkedHashSet() : super(_HashBase._INITIAL_INDEX_SIZE >> 1) {
	assert(_HashBase._UNUSED_PAIR == 0);
	}

	static Set<R> _newEmpty<R>() => new _CompactLinkedHashSet<R>();

	Set<R> cast<R>() => Set.castFrom<E, R>(this, newSet: _newEmpty);
	int get length => _usedData - _deletedKeys;

	E get first {
	for (int offset = 0; offset < _usedData; offset++) {
	Object current = _data[offset];
	if (!_HashBase._isDeleted(_data, current)) {
	return current;
	}
	}
	throw IterableElementError.noElement();
	}

	E get last {
	for (int offset = _usedData - 1; offset >= 0; offset--) {
	Object current = _data[offset];
	if (!_HashBase._isDeleted(_data, current)) {
	return current;
	}
	}
	throw IterableElementError.noElement();
	}

	void _rehash() {
	if ((_deletedKeys << 1) > _usedData) {
	_init(_index.length, _hashMask, _data, _usedData);
	} else {
	_init(_index.length << 1, _hashMask >> 1, _data, _usedData);
	}
	}

	void clear() {
	if (!isEmpty) {
	_init(_HashBase._INITIAL_INDEX_SIZE, _hashMask, null, 0);
	}
	}

	void _init(int size, int hashMask, List oldData, int oldUsed) {
	_index = new Uint32List(size);
	_hashMask = hashMask;
	_data = new List(size >> 1);
	_usedData = 0;
	_deletedKeys = 0;
	if (oldData != null) {
	for (int i = 0; i < oldUsed; i += 1) {
	var key = oldData[i];
	if (!_HashBase._isDeleted(oldData, key)) {
	add(key);
	}
	}
	}
	}

	bool add(E key) {
	final int size = _index.length;
	final int sizeMask = size - 1;
	final int maxEntries = size >> 1;
	final int fullHash = _hashCode(key);
	final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
	int i = _HashBase._firstProbe(fullHash, sizeMask);
	int firstDeleted = -1;
	int pair = _index[i];
	while (pair != _HashBase._UNUSED_PAIR) {
	if (pair == _HashBase._DELETED_PAIR) {
	if (firstDeleted < 0) {
	firstDeleted = i;
	}
	} else {
	final int d = hashPattern ^ pair;
	if (d < maxEntries && _equals(key, _data[d])) {
	return false;
	}
	}
	i = _HashBase._nextProbe(i, sizeMask);
	pair = _index[i];
	}
	if (_usedData == _data.length) {
	_rehash();
	add(key);
	} else {
	final int insertionPoint = (firstDeleted >= 0) ? firstDeleted : i;
	assert(1 <= hashPattern && hashPattern < (1 << 32));
	assert((hashPattern & _usedData) == 0);
	_index[insertionPoint] = hashPattern \| _usedData;
	_data[_usedData++] = key;
	}
	return true;
	}

	// If key is absent, return _data (which is never a value).
	Object _getKeyOrData(Object key) {
	final int size = _index.length;
	final int sizeMask = size - 1;
	final int maxEntries = size >> 1;
	final int fullHash = _hashCode(key);
	final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
	int i = _HashBase._firstProbe(fullHash, sizeMask);
	int pair = _index[i];
	while (pair != _HashBase._UNUSED_PAIR) {
	if (pair != _HashBase._DELETED_PAIR) {
	final int d = hashPattern ^ pair;
	if (d < maxEntries && _equals(key, _data[d])) {
	return _data[d]; // Note: Must return the existing key.
	}
	}
	i = _HashBase._nextProbe(i, sizeMask);
	pair = _index[i];
	}
	return _data;
	}

	E lookup(Object key) {
	var k = _getKeyOrData(key);
	return identical(_data, k) ? null : k;
	}

	bool contains(Object key) => !identical(_data, _getKeyOrData(key));

	bool remove(Object key) {
	final int size = _index.length;
	final int sizeMask = size - 1;
	final int maxEntries = size >> 1;
	final int fullHash = _hashCode(key);
	final int hashPattern = _HashBase._hashPattern(fullHash, _hashMask, size);
	int i = _HashBase._firstProbe(fullHash, sizeMask);
	int pair = _index[i];
	while (pair != _HashBase._UNUSED_PAIR) {
	if (pair != _HashBase._DELETED_PAIR) {
	final int d = hashPattern ^ pair;
	if (d < maxEntries && _equals(key, _data[d])) {
	_index[i] = _HashBase._DELETED_PAIR;
	_HashBase._setDeletedAt(_data, d);
	++_deletedKeys;
	return true;
	}
	}
	i = _HashBase._nextProbe(i, sizeMask);
	pair = _index[i];
	}
	return false;
	}

	Iterator<E> get iterator =>
	new _CompactIterator<E>(this, _data, _usedData, -1, 1);

	// Returns a set of the same type, although this
	// is not required by the spec. (For instance, always using an identity set
	// would be technically correct, albeit surprising.)
	Set<E> toSet() => new _CompactLinkedHashSet<E>()..addAll(this);
	}

	class _CompactLinkedIdentityHashSet<E> extends _CompactLinkedHashSet<E>
	with _IdenticalAndIdentityHashCode {
	Set<E> toSet() => new _CompactLinkedIdentityHashSet<E>()..addAll(this);

	static Set<R> _newEmpty<R>() => new _CompactLinkedIdentityHashSet<R>();

	Set<R> cast<R>() => Set.castFrom<E, R>(this, newSet: _newEmpty);
	}

	class _CompactLinkedCustomHashSet<E> extends _CompactLinkedHashSet<E> {
	final _equality;
	final _hasher;
	final _validKey;

	int _hashCode(e) => _hasher(e);
	bool _equals(e1, e2) => _equality(e1, e2);

	bool contains(Object o) => _validKey(o) ? super.contains(o) : false;
	E lookup(Object o) => _validKey(o) ? super.lookup(o) : null;
	bool remove(Object o) => _validKey(o) ? super.remove(o) : false;

	_CompactLinkedCustomHashSet(this._equality, this._hasher, validKey)
	: _validKey = (validKey != null) ? validKey : new _TypeTest<E>().test;

	Set<R> cast<R>() => Set.castFrom<E, R>(this);
	Set<E> toSet() =>
	new _CompactLinkedCustomHashSet<E>(_equality, _hasher, _validKey)
	..addAll(this);
	}