1/****************************************************************************
2**
3** Copyright (C) 2016 The Qt Company Ltd.
4** Contact: https://www.qt.io/licensing/
5**
6** This file is part of the QtQml module of the Qt Toolkit.
7**
8** $QT_BEGIN_LICENSE:LGPL$
9** Commercial License Usage
10** Licensees holding valid commercial Qt licenses may use this file in
11** accordance with the commercial license agreement provided with the
12** Software or, alternatively, in accordance with the terms contained in
13** a written agreement between you and The Qt Company. For licensing terms
14** and conditions see https://www.qt.io/terms-conditions. For further
15** information use the contact form at https://www.qt.io/contact-us.
16**
17** GNU Lesser General Public License Usage
18** Alternatively, this file may be used under the terms of the GNU Lesser
19** General Public License version 3 as published by the Free Software
20** Foundation and appearing in the file LICENSE.LGPL3 included in the
21** packaging of this file. Please review the following information to
22** ensure the GNU Lesser General Public License version 3 requirements
23** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
24**
25** GNU General Public License Usage
26** Alternatively, this file may be used under the terms of the GNU
27** General Public License version 2.0 or (at your option) the GNU General
28** Public license version 3 or any later version approved by the KDE Free
29** Qt Foundation. The licenses are as published by the Free Software
30** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
31** included in the packaging of this file. Please review the following
32** information to ensure the GNU General Public License requirements will
33** be met: https://www.gnu.org/licenses/gpl-2.0.html and
34** https://www.gnu.org/licenses/gpl-3.0.html.
35**
36** $QT_END_LICENSE$
37**
38****************************************************************************/
39
40#include "qv4memberdata_p.h"
41#include <private/qv4mm_p.h>
42#include "qv4value_p.h"
43
44using namespace QV4;
45
46DEFINE_MANAGED_VTABLE(MemberData);
47
48static size_t nextPowerOfTwo(size_t s)
49{
50 --s;
51 s |= s >> 1;
52 s |= s >> 2;
53 s |= s >> 4;
54 s |= s >> 8;
55 s |= s >> 16;
56#if (QT_POINTER_SIZE == 8)
57 s |= s >> 32;
58#endif
59 ++s;
60 return s;
61}
62
63Heap::MemberData *MemberData::allocate(ExecutionEngine *e, uint n, Heap::MemberData *old)
64{
65 Q_ASSERT(!old || old->values.size <= n);
66 if (!n)
67 n = 4;
68
69 size_t alloc = MemoryManager::align(size: sizeof(Heap::MemberData) + (n - 1)*sizeof(Value));
70 // round up to next power of two to avoid quadratic behaviour for very large objects
71 alloc = nextPowerOfTwo(s: alloc);
72
73 // The above code can overflow in a number of interesting ways. All of those are unsigned,
74 // and therefore defined behavior. Still, apply some sane bounds.
75 const size_t intMax = std::numeric_limits<int>::max();
76 if (alloc > intMax)
77 alloc = intMax;
78
79 Heap::MemberData *m;
80 if (old) {
81 const size_t oldSize = sizeof(Heap::MemberData) + (old->values.size - 1) * sizeof(Value);
82 if (oldSize > alloc)
83 alloc = oldSize;
84 m = e->memoryManager->allocManaged<MemberData>(size: alloc);
85 // no write barrier required here
86 memcpy(dest: m, src: old, n: oldSize);
87 } else {
88 m = e->memoryManager->allocManaged<MemberData>(size: alloc);
89 m->init();
90 }
91
92 m->values.alloc = static_cast<uint>((alloc - sizeof(Heap::MemberData) + sizeof(Value))/sizeof(Value));
93 m->values.size = m->values.alloc;
94 return m;
95}
96

source code of qtdeclarative/src/qml/jsruntime/qv4memberdata.cpp