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// Copyright (C) 2020 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#ifndef QDUPLICATETRACKER_P_H
#define QDUPLICATETRACKER_P_H
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
#include <private/qglobal_p.h>
#ifdef __cpp_lib_memory_resource
# include <unordered_set>
# include <memory_resource>
# include <qhash.h> // for the hashing helpers
#else
# include <qset.h>
#endif
QT_BEGIN_NAMESPACE
template <typename T, size_t Prealloc = 32>
class QDuplicateTracker {
#ifdef __cpp_lib_memory_resource
template <typename HT>
struct QHasher {
size_t storedSeed = QHashSeed::globalSeed();
size_t operator()(const HT &t) const {
return QHashPrivate::calculateHash(t, storedSeed);
}
};
struct node_guesstimate { void *next; size_t hash; T value; };
static constexpr size_t bufferSize(size_t N) {
return N * sizeof(void*) // bucket list
+ N * sizeof(node_guesstimate); // nodes
}
char buffer[bufferSize(Prealloc)];
std::pmr::monotonic_buffer_resource res{buffer, sizeof buffer};
using Set = std::pmr::unordered_set<T, QHasher<T>>;
Set set{Prealloc, &res};
#else
class Set : public QSet<T> {
qsizetype setSize = 0;
public:
explicit Set(qsizetype n) : QSet<T>{}
{ this->reserve(n); }
auto insert(const T &e) {
auto it = QSet<T>::insert(e);
const auto n = this->size();
return std::pair{it, std::exchange(setSize, n) != n};
}
auto insert(T &&e) {
auto it = QSet<T>::insert(std::move(e));
const auto n = this->size();
return std::pair{it, std::exchange(setSize, n) != n};
}
};
Set set{Prealloc};
#endif
Q_DISABLE_COPY_MOVE(QDuplicateTracker)
public:
static constexpr inline bool uses_pmr =
#ifdef __cpp_lib_memory_resource
true
#else
false
#endif
;
QDuplicateTracker() {} // don't `= default`, lest we value-initialize `buffer`
explicit QDuplicateTracker(qsizetype n)
#ifdef __cpp_lib_memory_resource
: set{size_t(n), &res}
#else
: set{n}
#endif
{}
Q_DECL_DEPRECATED_X("Pass the capacity to reserve() to the ctor instead.")
void reserve(qsizetype n) { set.reserve(n); }
[[nodiscard]] bool hasSeen(const T &s)
{
return !set.insert(s).second;
}
[[nodiscard]] bool hasSeen(T &&s)
{
return !set.insert(std::move(s)).second;
}
// For when you want to know, but aren't *yet* sure you'll add it:
[[nodiscard]] bool contains(const T &s) const
{
return set.find(s) != set.end(); // TODO C++20: can use set.contains()
}
template <typename C>
void appendTo(C &c) const &
{
for (const auto &e : set)
c.push_back(e);
}
template <typename C>
void appendTo(C &c) &&
{
if constexpr (uses_pmr) {
while (!set.empty())
c.push_back(std::move(set.extract(set.begin()).value()));
} else {
return appendTo(c); // lvalue version
}
}
void clear()
{
#ifdef __cpp_lib_memory_resource
// The birth defect of std::unordered_set is that both the nodes as
// well as the bucket array are allocated from the same allocator, so
// if we want to reclaim memory from the freed nodes, we also need to
// reclaim the memory for the bucket array.
set = Set(); // release all memory in `res` (clear() doesn't, and swap() is UB!)
res.release(); // restore to initial state (buffer, sizeof buffer)
// m_b_r can't reuse buffers, anyway
// now that `res` is reset to the initial state, also reset `set`:
set = Set{Prealloc, &res};
#else
set.clear();
#endif // __cpp_lib_memory_resource
}
using const_iterator = typename Set::const_iterator;
const_iterator begin() const { return set.cbegin(); }
const_iterator end() const { return set.cend(); }
const_iterator cbegin() const { return begin(); }
const_iterator cend() const { return end(); }
};
QT_END_NAMESPACE
#endif /* QDUPLICATETRACKER_P_H */
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