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      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/unicode/Unicode.h>
     30 
     31 namespace WTF {
     32 
     33 class StringImplBase {
     34     WTF_MAKE_NONCOPYABLE(StringImplBase); WTF_MAKE_FAST_ALLOCATED;
     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     // For SmallStringStorage, which allocates an array and uses an in-place new.
     49     StringImplBase() { }
     50 
     51     StringImplBase(unsigned length, BufferOwnership ownership)
     52         : m_refCountAndFlags(s_refCountIncrement | s_refCountFlagShouldReportedCost | ownership)
     53         , m_length(length)
     54     {
     55         ASSERT(isStringImpl());
     56     }
     57 
     58     enum StaticStringConstructType { ConstructStaticString };
     59     StringImplBase(unsigned length, StaticStringConstructType)
     60         : m_refCountAndFlags(s_refCountFlagStatic | s_refCountFlagIsIdentifier | BufferOwned)
     61         , m_length(length)
     62     {
     63         ASSERT(isStringImpl());
     64     }
     65 
     66     // This constructor is not used when creating StringImpl objects,
     67     // and sets the flags into a state marking the object as such.
     68     enum NonStringImplConstructType { ConstructNonStringImpl };
     69     StringImplBase(NonStringImplConstructType)
     70         : m_refCountAndFlags(s_refCountIncrement | s_refCountInvalidForStringImpl)
     71         , m_length(0)
     72     {
     73         ASSERT(!isStringImpl());
     74     }
     75 
     76     // The bottom 7 bits hold flags, the top 25 bits hold the ref count.
     77     // When dereferencing StringImpls we check for the ref count AND the
     78     // static bit both being zero - static strings are never deleted.
     79     static const unsigned s_refCountMask = 0xFFFFFF80;
     80     static const unsigned s_refCountIncrement = 0x80;
     81     static const unsigned s_refCountFlagStatic = 0x40;
     82     static const unsigned s_refCountFlagHasTerminatingNullCharacter = 0x20;
     83     static const unsigned s_refCountFlagIsAtomic = 0x10;
     84     static const unsigned s_refCountFlagShouldReportedCost = 0x8;
     85     static const unsigned s_refCountFlagIsIdentifier = 0x4;
     86     static const unsigned s_refCountMaskBufferOwnership = 0x3;
     87     // An invalid permutation of flags (static & shouldReportedCost - static strings do not
     88     // set shouldReportedCost in the constructor, and this bit is only ever cleared, not set).
     89     // Used by "ConstructNonStringImpl" constructor, above.
     90     static const unsigned s_refCountInvalidForStringImpl = s_refCountFlagStatic | s_refCountFlagShouldReportedCost;
     91 
     92     unsigned m_refCountAndFlags;
     93     unsigned m_length;
     94 };
     95 
     96 } // namespace WTF
     97 
     98 using WTF::StringImplBase;
     99 
    100 #endif
    101