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
31namespace WTF {
32
33class StringImplBase {
34    WTF_MAKE_NONCOPYABLE(StringImplBase); WTF_MAKE_FAST_ALLOCATED;
35public:
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
40protected:
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
98using WTF::StringImplBase;
99
100#endif
101