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      1 /*
      2  * Copyright (C) 2007, 2008 Apple Inc. All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions
      6  * are met:
      7  *
      8  * 1.  Redistributions of source code must retain the above copyright
      9  *     notice, this list of conditions and the following disclaimer.
     10  * 2.  Redistributions in binary form must reproduce the above copyright
     11  *     notice, this list of conditions and the following disclaimer in the
     12  *     documentation and/or other materials provided with the distribution.
     13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
     14  *     its contributors may be used to endorse or promote products derived
     15  *     from this software without specific prior written permission.
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
     18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
     21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #ifndef SymbolTable_h
     30 #define SymbolTable_h
     31 
     32 #include "JSObject.h"
     33 #include "UString.h"
     34 #include <wtf/AlwaysInline.h>
     35 
     36 namespace JSC {
     37 
     38     static ALWAYS_INLINE int missingSymbolMarker() { return std::numeric_limits<int>::max(); }
     39 
     40     // The bit twiddling in this class assumes that every register index is a
     41     // reasonably small positive or negative number, and therefore has its high
     42     // four bits all set or all unset.
     43 
     44     struct SymbolTableEntry {
     45         SymbolTableEntry()
     46             : m_bits(0)
     47         {
     48         }
     49 
     50         SymbolTableEntry(int index)
     51         {
     52             ASSERT(isValidIndex(index));
     53             pack(index, false, false);
     54         }
     55 
     56         SymbolTableEntry(int index, unsigned attributes)
     57         {
     58             ASSERT(isValidIndex(index));
     59             pack(index, attributes & ReadOnly, attributes & DontEnum);
     60         }
     61 
     62         bool isNull() const
     63         {
     64             return !m_bits;
     65         }
     66 
     67         int getIndex() const
     68         {
     69             return m_bits >> FlagBits;
     70         }
     71 
     72         unsigned getAttributes() const
     73         {
     74             unsigned attributes = 0;
     75             if (m_bits & ReadOnlyFlag)
     76                 attributes |= ReadOnly;
     77             if (m_bits & DontEnumFlag)
     78                 attributes |= DontEnum;
     79             return attributes;
     80         }
     81 
     82         void setAttributes(unsigned attributes)
     83         {
     84             pack(getIndex(), attributes & ReadOnly, attributes & DontEnum);
     85         }
     86 
     87         bool isReadOnly() const
     88         {
     89             return m_bits & ReadOnlyFlag;
     90         }
     91 
     92     private:
     93         static const unsigned ReadOnlyFlag = 0x1;
     94         static const unsigned DontEnumFlag = 0x2;
     95         static const unsigned NotNullFlag = 0x4;
     96         static const unsigned FlagBits = 3;
     97 
     98         void pack(int index, bool readOnly, bool dontEnum)
     99         {
    100             m_bits = (index << FlagBits) | NotNullFlag;
    101             if (readOnly)
    102                 m_bits |= ReadOnlyFlag;
    103             if (dontEnum)
    104                 m_bits |= DontEnumFlag;
    105         }
    106 
    107         bool isValidIndex(int index)
    108         {
    109             return ((index << FlagBits) >> FlagBits) == index;
    110         }
    111 
    112         int m_bits;
    113     };
    114 
    115     struct SymbolTableIndexHashTraits {
    116         typedef SymbolTableEntry TraitType;
    117         static SymbolTableEntry emptyValue() { return SymbolTableEntry(); }
    118         static const bool emptyValueIsZero = true;
    119         static const bool needsDestruction = false;
    120     };
    121 
    122     typedef HashMap<RefPtr<UString::Rep>, SymbolTableEntry, IdentifierRepHash, HashTraits<RefPtr<UString::Rep> >, SymbolTableIndexHashTraits> SymbolTable;
    123 
    124     class SharedSymbolTable : public SymbolTable, public RefCounted<SharedSymbolTable>
    125     {
    126     };
    127 
    128 } // namespace JSC
    129 
    130 #endif // SymbolTable_h
    131