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      1 /*
      2  *  Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
      3  *
      4  *  This library is free software; you can redistribute it and/or
      5  *  modify it under the terms of the GNU Library General Public
      6  *  License as published by the Free Software Foundation; either
      7  *  version 2 of the License, or (at your option) any later version.
      8  *
      9  *  This library is distributed in the hope that it will be useful,
     10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
     11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     12  *  Library General Public License for more details.
     13  *
     14  *  You should have received a copy of the GNU Library General Public License
     15  *  along with this library; see the file COPYING.LIB.  If not, write to
     16  *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
     17  *  Boston, MA 02110-1301, USA.
     18  *
     19  */
     20 
     21 #ifndef PropertyMapHashTable_h
     22 #define PropertyMapHashTable_h
     23 
     24 #include "UString.h"
     25 #include <wtf/Vector.h>
     26 
     27 namespace JSC {
     28 
     29     struct PropertyMapEntry {
     30         UString::Rep* key;
     31         unsigned offset;
     32         unsigned attributes;
     33         JSCell* specificValue;
     34         unsigned index;
     35 
     36         PropertyMapEntry(UString::Rep* key, unsigned attributes, JSCell* specificValue)
     37             : key(key)
     38             , offset(0)
     39             , attributes(attributes)
     40             , specificValue(specificValue)
     41             , index(0)
     42         {
     43         }
     44 
     45         PropertyMapEntry(UString::Rep* key, unsigned offset, unsigned attributes, JSCell* specificValue, unsigned index)
     46             : key(key)
     47             , offset(offset)
     48             , attributes(attributes)
     49             , specificValue(specificValue)
     50             , index(index)
     51         {
     52         }
     53     };
     54 
     55     // lastIndexUsed is an ever-increasing index used to identify the order items
     56     // were inserted into the property map. It's required that getEnumerablePropertyNames
     57     // return the properties in the order they were added for compatibility with other
     58     // browsers' JavaScript implementations.
     59     struct PropertyMapHashTable {
     60         unsigned sizeMask;
     61         unsigned size;
     62         unsigned keyCount;
     63         unsigned deletedSentinelCount;
     64         unsigned lastIndexUsed;
     65         Vector<unsigned>* deletedOffsets;
     66         unsigned entryIndices[1];
     67 
     68         PropertyMapEntry* entries()
     69         {
     70             // The entries vector comes after the indices vector.
     71             // The 0th item in the entries vector is not really used; it has to
     72             // have a 0 in its key to allow the hash table lookup to handle deleted
     73             // sentinels without any special-case code, but the other fields are unused.
     74             return reinterpret_cast<PropertyMapEntry*>(&entryIndices[size]);
     75         }
     76 
     77         static size_t allocationSize(unsigned size)
     78         {
     79             // We never let a hash table get more than half full,
     80             // So the number of indices we need is the size of the hash table.
     81             // But the number of entries is half that (plus one for the deleted sentinel).
     82             return sizeof(PropertyMapHashTable)
     83                 + (size - 1) * sizeof(unsigned)
     84                 + (1 + size / 2) * sizeof(PropertyMapEntry);
     85         }
     86     };
     87 
     88 } // namespace JSC
     89 
     90 #endif // PropertyMapHashTable_h
     91