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 #include <wtf/HashTraits.h>
  36
  37 namespace JSC {
  38
  39     static ALWAYS_INLINE int missingSymbolMarker() { return std::numeric_limits<int>::max(); }
  40
  41     // The bit twiddling in this class assumes that every register index is a
  42     // reasonably small positive or negative number, and therefore has its high
  43     // four bits all set or all unset.
  44
  45     struct SymbolTableEntry {
  46         SymbolTableEntry()
  47             : m_bits(0)
  48         {
  49         }
  50
  51         SymbolTableEntry(int index)
  52         {
  53             ASSERT(isValidIndex(index));
  54             pack(index, false, false);
  55         }
  56
  57         SymbolTableEntry(int index, unsigned attributes)
  58         {
  59             ASSERT(isValidIndex(index));
  60             pack(index, attributes & ReadOnly, attributes & DontEnum);
  61         }
  62
  63         bool isNull() const
  64         {
  65             return !m_bits;
  66         }
  67
  68         int getIndex() const
  69         {
  70             return m_bits >> FlagBits;
  71         }
  72
  73         unsigned getAttributes() const
  74         {
  75             unsigned attributes = 0;
  76             if (m_bits & ReadOnlyFlag)
  77                 attributes |= ReadOnly;
  78             if (m_bits & DontEnumFlag)
  79                 attributes |= DontEnum;
  80             return attributes;
  81         }
  82
  83         void setAttributes(unsigned attributes)
  84         {
  85             pack(getIndex(), attributes & ReadOnly, attributes & DontEnum);
  86         }
  87
  88         bool isReadOnly() const
  89         {
  90             return m_bits & ReadOnlyFlag;
  91         }
  92
  93     private:
  94         static const unsigned ReadOnlyFlag = 0x1;
  95         static const unsigned DontEnumFlag = 0x2;
  96         static const unsigned NotNullFlag = 0x4;
  97         static const unsigned FlagBits = 3;
  98
  99         void pack(int index, bool readOnly, bool dontEnum)
 100         {
 101             m_bits = (index << FlagBits) | NotNullFlag;
 102             if (readOnly)
 103                 m_bits |= ReadOnlyFlag;
 104             if (dontEnum)
 105                 m_bits |= DontEnumFlag;
 106         }
 107
 108         bool isValidIndex(int index)
 109         {
 110             return ((index << FlagBits) >> FlagBits) == index;
 111         }
 112
 113         int m_bits;
 114     };
 115
 116     struct SymbolTableIndexHashTraits : HashTraits<SymbolTableEntry> {
 117         static const bool emptyValueIsZero = true;
 118         static const bool needsDestruction = false;
 119     };
 120
 121     typedef HashMap<RefPtr<StringImpl>, SymbolTableEntry, IdentifierRepHash, HashTraits<RefPtr<StringImpl> >, SymbolTableIndexHashTraits> SymbolTable;
 122
 123     class SharedSymbolTable : public SymbolTable, public RefCounted<SharedSymbolTable> {
 124         WTF_MAKE_FAST_ALLOCATED;
 125     public:
 126         static PassRefPtr<SharedSymbolTable> create() { return adoptRef(new SharedSymbolTable); }
 127     private:
 128         SharedSymbolTable() { turnOffVerifier(); }
 129     };
 130
 131 } // namespace JSC
 132
 133 #endif // SymbolTable_h