runtime/SymbolTable.h

   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