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3** Copyright (C) 2020 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
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39#ifndef QDUPLICATETRACKER_P_H
40#define QDUPLICATETRACKER_P_H
41
42//
43// W A R N I N G
44// -------------
45//
46// This file is not part of the Qt API. It exists purely as an
47// implementation detail. This header file may change from version to
48// version without notice, or even be removed.
49//
50// We mean it.
51//
52
53#include <qglobal.h>
54
55#if QT_HAS_INCLUDE(<memory_resource>) && __cplusplus > 201402L
56# include <unordered_set>
57# include <memory_resource>
58#else
59# include <qset.h>
60#endif
61
62QT_BEGIN_NAMESPACE
63
64template <typename T, size_t Prealloc = 32>
65class QDuplicateTracker {
66#ifdef __cpp_lib_memory_resource
67 struct node_guesstimate { void *next; size_t hash; T value; };
68 static constexpr size_t bufferSize(size_t N) {
69 return N * sizeof(void*) // bucket list
70 + N * sizeof(node_guesstimate); // nodes
71 }
72
73 char buffer[bufferSize(N: Prealloc)];
74 std::pmr::monotonic_buffer_resource res{buffer, sizeof buffer};
75 std::pmr::unordered_set<T> set{Prealloc, &res};
76#else
77 static QSet<T> makeQSet() { QSet<T> r; r.reserve(Prealloc); return r; }
78 QSet<T> set = makeQSet();
79 int setSize = 0;
80#endif
81 Q_DISABLE_COPY_MOVE(QDuplicateTracker);
82public:
83 QDuplicateTracker() = default;
84 void reserve(int n) { set.reserve(n); }
85 Q_REQUIRED_RESULT bool hasSeen(const T &s)
86 {
87 bool inserted;
88#ifdef __cpp_lib_memory_resource
89 inserted = set.insert(s).second;
90#else
91 set.insert(s);
92 const int n = set.size();
93 inserted = qExchange(setSize, n) != n;
94#endif
95 return !inserted;
96 }
97};
98
99QT_END_NAMESPACE
100
101#endif /* QDUPLICATETRACKER_P_H */
102

source code of qtbase/src/corelib/tools/qduplicatetracker_p.h