1 /*

     2  * Copyright (C) 2010 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  * 1. Redistributions of source code must retain the above copyright

     8  *    notice, this list of conditions and the following disclaimer.

     9  * 2. Redistributions in binary form must reproduce the above copyright

    10  *    notice, this list of conditions and the following disclaimer in the

    11  *    documentation and/or other materials provided with the distribution.

    12  *

    13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY

    14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

    15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

    16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR

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

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

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

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

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

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

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

    24  */

    25 

    26 #ifndef StringImplBase_h

    27 #define StringImplBase_h

    28 

    29 #include <wtf/Noncopyable.h>

    30 #include <wtf/unicode/Unicode.h>

    31 

    32 namespace WTF {

    33 

    34 class StringImplBase : public Noncopyable {

    35 public:

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

    37     unsigned length() const { return m_length; }

    38     void ref() { m_refCountAndFlags += s_refCountIncrement; }

    39 

    40 protected:

    41     enum BufferOwnership {

    42         BufferInternal,

    43         BufferOwned,

    44         BufferSubstring,

    45         BufferShared,

    46     };

    47 

    48     using Noncopyable::operator new;

    49 

    50 #if !COMPILER(WINSCW)

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

    52 #endif

    53 

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

    55     StringImplBase() { }

    56 

    57     StringImplBase(unsigned length, BufferOwnership ownership)

    58         : m_refCountAndFlags(s_refCountIncrement | s_refCountFlagShouldReportedCost | ownership)

    59         , m_length(length)

    60     {

    61         ASSERT(isStringImpl());

    62     }

    63 

    64     enum StaticStringConstructType { ConstructStaticString };

    65     StringImplBase(unsigned length, StaticStringConstructType)

    66         : m_refCountAndFlags(s_refCountFlagStatic | s_refCountFlagIsIdentifier | BufferOwned)

    67         , m_length(length)

    68     {

    69         ASSERT(isStringImpl());

    70     }

    71 

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

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

    74     enum NonStringImplConstructType { ConstructNonStringImpl };

    75     StringImplBase(NonStringImplConstructType)

    76         : m_refCountAndFlags(s_refCountIncrement | s_refCountInvalidForStringImpl)

    77         , m_length(0)

    78     {

    79         ASSERT(!isStringImpl());

    80     }

    81 

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

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

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

    85     static const unsigned s_refCountMask = 0xFFFFFF80;

    86     static const unsigned s_refCountIncrement = 0x80;

    87     static const unsigned s_refCountFlagStatic = 0x40;

    88     static const unsigned s_refCountFlagHasTerminatingNullCharacter = 0x20;

    89     static const unsigned s_refCountFlagIsAtomic = 0x10;

    90     static const unsigned s_refCountFlagShouldReportedCost = 0x8;

    91     static const unsigned s_refCountFlagIsIdentifier = 0x4;

    92     static const unsigned s_refCountMaskBufferOwnership = 0x3;

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

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

    95     // Used by "ConstructNonStringImpl" constructor, above.

    96     static const unsigned s_refCountInvalidForStringImpl = s_refCountFlagStatic | s_refCountFlagShouldReportedCost;

    97 

    98     unsigned m_refCountAndFlags;

    99     unsigned m_length;

   100 };

   101 

   102 } // namespace WTF

   103 

   104 using WTF::StringImplBase;

   105 

   106 #endif