wtf/text/StringImplBase.h

   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