JavaScriptCore-1097.3.3.tar.gz

[apple/javascriptcore.git] / runtime / SymbolTable.h

/*
 * Copyright (C) 2007, 2008 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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 */

#ifndef SymbolTable_h
#define SymbolTable_h

#include "JSObject.h"
#include "UString.h"
#include <wtf/AlwaysInline.h>
#include <wtf/HashTraits.h>

namespace JSC {

    static ALWAYS_INLINE int missingSymbolMarker() { return std::numeric_limits<int>::max(); }

    // The bit twiddling in this class assumes that every register index is a
    // reasonably small positive or negative number, and therefore has its high
    // four bits all set or all unset.

    struct SymbolTableEntry {
        SymbolTableEntry()
            : m_bits(0)
        {
        }

        SymbolTableEntry(int index)
        {
            ASSERT(isValidIndex(index));
            pack(index, false, false);
        }

        SymbolTableEntry(int index, unsigned attributes)
        {
            ASSERT(isValidIndex(index));
            pack(index, attributes & ReadOnly, attributes & DontEnum);
        }
        
        bool isNull() const
        {
            return !m_bits;
        }

        int getIndex() const
        {
            return m_bits >> FlagBits;
        }

        unsigned getAttributes() const
        {
            unsigned attributes = 0;
            if (m_bits & ReadOnlyFlag)
                attributes |= ReadOnly;
            if (m_bits & DontEnumFlag)
                attributes |= DontEnum;
            return attributes;
        }

        void setAttributes(unsigned attributes)
        {
            pack(getIndex(), attributes & ReadOnly, attributes & DontEnum);
        }

        bool isReadOnly() const
        {
            return m_bits & ReadOnlyFlag;
        }

    private:
        static const unsigned ReadOnlyFlag = 0x1;
        static const unsigned DontEnumFlag = 0x2;
        static const unsigned NotNullFlag = 0x4;
        static const unsigned FlagBits = 3;

        void pack(int index, bool readOnly, bool dontEnum)
        {
            m_bits = (index << FlagBits) | NotNullFlag;
            if (readOnly)
                m_bits |= ReadOnlyFlag;
            if (dontEnum)
                m_bits |= DontEnumFlag;
        }
        
        bool isValidIndex(int index)
        {
            return ((index << FlagBits) >> FlagBits) == index;
        }

        int m_bits;
    };

    struct SymbolTableIndexHashTraits : HashTraits<SymbolTableEntry> {
        static const bool emptyValueIsZero = true;
        static const bool needsDestruction = false;
    };

    typedef HashMap<RefPtr<StringImpl>, SymbolTableEntry, IdentifierRepHash, HashTraits<RefPtr<StringImpl> >, SymbolTableIndexHashTraits> SymbolTable;

    class SharedSymbolTable : public SymbolTable, public RefCounted<SharedSymbolTable> {
        WTF_MAKE_FAST_ALLOCATED;
    public:
        static PassRefPtr<SharedSymbolTable> create() { return adoptRef(new SharedSymbolTable); }
    private:
        SharedSymbolTable() { turnOffVerifier(); }
    };
    
} // namespace JSC

#endif // SymbolTable_h