/*

 * Copyright (C) 2010 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.

 *

 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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 DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR

 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,

 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR

 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY

 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 

 */

#ifndef StringImplBase_h

#define StringImplBase_h

#include <wtf/Noncopyable.h>

#include <wtf/unicode/Unicode.h>

namespace WTF {

class StringImplBase : public Noncopyable {

public:

    bool isStringImpl() { return (m_refCountAndFlags & s_refCountInvalidForStringImpl) != s_refCountInvalidForStringImpl; }

    unsigned length() const { return m_length; }

    void ref() { m_refCountAndFlags += s_refCountIncrement; }

protected:

    enum BufferOwnership {

        BufferInternal,

        BufferOwned,

        BufferSubstring,

        BufferShared,

    };

    using Noncopyable::operator new;

#if !COMPILER(WINSCW)

    void* operator new(size_t, void* inPlace) { ASSERT(inPlace); return inPlace; }

#endif

    // For SmallStringStorage, which allocates an array and uses an in-place new.

    StringImplBase() { }

    StringImplBase(unsigned length, BufferOwnership ownership)

        : m_refCountAndFlags(s_refCountIncrement | s_refCountFlagShouldReportedCost | ownership)

        , m_length(length)

    {

        ASSERT(isStringImpl());

    }

    enum StaticStringConstructType { ConstructStaticString };

    StringImplBase(unsigned length, StaticStringConstructType)

        : m_refCountAndFlags(s_refCountFlagStatic | s_refCountFlagIsIdentifier | BufferOwned)

        , m_length(length)

    {

        ASSERT(isStringImpl());

    }

    // This constructor is not used when creating StringImpl objects,

    // and sets the flags into a state marking the object as such.

    enum NonStringImplConstructType { ConstructNonStringImpl };

    StringImplBase(NonStringImplConstructType)

        : m_refCountAndFlags(s_refCountIncrement | s_refCountInvalidForStringImpl)

        , m_length(0)

    {

        ASSERT(!isStringImpl());

    }

    // The bottom 7 bits hold flags, the top 25 bits hold the ref count.

    // When dereferencing StringImpls we check for the ref count AND the

    // static bit both being zero - static strings are never deleted.

    static const unsigned s_refCountMask = 0xFFFFFF80;

    static const unsigned s_refCountIncrement = 0x80;

    static const unsigned s_refCountFlagStatic = 0x40;

    static const unsigned s_refCountFlagHasTerminatingNullCharacter = 0x20;

    static const unsigned s_refCountFlagIsAtomic = 0x10;

    static const unsigned s_refCountFlagShouldReportedCost = 0x8;

    static const unsigned s_refCountFlagIsIdentifier = 0x4;

    static const unsigned s_refCountMaskBufferOwnership = 0x3;

    // An invalid permutation of flags (static & shouldReportedCost - static strings do not

    // set shouldReportedCost in the constructor, and this bit is only ever cleared, not set).

    // Used by "ConstructNonStringImpl" constructor, above.

    static const unsigned s_refCountInvalidForStringImpl = s_refCountFlagStatic | s_refCountFlagShouldReportedCost;

    unsigned m_refCountAndFlags;

    unsigned m_length;

};

} // namespace WTF

using WTF::StringImplBase;

#endif