mirror of https://github.com/JakubMelka/PDF4QT.git
131 lines
4.1 KiB
C++
131 lines
4.1 KiB
C++
// Copyright (C) 2018-2021 Jakub Melka
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//
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// This file is part of PDF4QT.
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//
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// PDF4QT is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// with the written consent of the copyright owner, any later version.
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//
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// PDF4QT is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with PDF4QT. If not, see <https://www.gnu.org/licenses/>.
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#ifndef PDFFLATMAP_H
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#define PDFFLATMAP_H
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#include <set>
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#include <array>
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#include <algorithm>
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namespace pdf
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{
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/// This class behaves like std::set, but have "flat" part, and if size of the set
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/// is small (smaller than \p FlatSize), then no memory allocation is needed. This
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/// container supports inserting, deleting and searching for the object presence.
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template<typename Key, int FlatSize>
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class PDFFlatMap
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{
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public:
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constexpr inline PDFFlatMap();
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/// Inserts a key in the container. Checks, if key is already present
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/// in the container, in this case no insertion occurs.
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/// \param key Key to be inserted
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void insert(const Key& key);
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/// Erases a key in the container, if it is in the set
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/// \param key Key to be erased
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void erase(const Key& key);
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/// Searchs for a given key. If it is found, true is returned, false otherwise.
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/// \param key Key to be searched
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bool search(const Key& key) const;
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/// Returns size of the container
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std::size_t size() const;
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/// Returns true, if container is empty
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bool empty() const;
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private:
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/// Flat part of the set
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std::array<Key, FlatSize> m_flat;
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/// This iterator points to first empty position, or it is
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/// the last iterator (pointing to the end of the array).
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typename std::array<Key, FlatSize>::iterator m_flatEmptyPosition;
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std::set<Key> m_overflowContainer;
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};
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template<typename Key, int FlatSize>
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constexpr PDFFlatMap<Key, FlatSize>::PDFFlatMap() :
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m_flat(),
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m_flatEmptyPosition(m_flat.begin()),
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m_overflowContainer()
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{
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}
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template<typename Key, int FlatSize>
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void PDFFlatMap<Key, FlatSize>::insert(const Key& key)
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{
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if (!search(key))
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{
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// Try to insert key in the flat part, if possible (we are not at end of the array)
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if (m_flatEmptyPosition != m_flat.end())
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{
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*m_flatEmptyPosition++ = key;
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}
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else
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{
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m_overflowContainer.insert(key);
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}
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}
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}
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template<typename Key, int FlatSize>
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void PDFFlatMap<Key, FlatSize>::erase(const Key& key)
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{
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// First we must check, if the key is present in the flat part. If yes, then remove key
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// from the flat part and try to move one item from the overflow part to the flat part, if possible.
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// Otherwise check overflow part.
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m_flatEmptyPosition = std::remove_if(m_flat.begin(), m_flatEmptyPosition, [&key](const Key& otherKey) { return key == otherKey; });
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m_overflowContainer.erase(key);
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if (!m_overflowContainer.empty() && m_flatEmptyPosition != m_flat.end())
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{
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*m_flatEmptyPosition++ = *m_overflowContainer.begin();
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m_overflowContainer.erase(m_overflowContainer.begin());
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}
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}
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template<typename Key, int FlatSize>
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bool PDFFlatMap<Key, FlatSize>::search(const Key& key) const
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{
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return std::find<typename std::array<Key, FlatSize>::const_iterator, Key>(m_flat.begin(), m_flatEmptyPosition, key) != m_flatEmptyPosition || static_cast<bool>(m_overflowContainer.count(key));
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}
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template<typename Key, int FlatSize>
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std::size_t PDFFlatMap<Key, FlatSize>::size() const
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{
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return std::distance<typename std::array<Key, FlatSize>::const_iterator>(m_flat.begin(), m_flatEmptyPosition) + m_overflowContainer.size();
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}
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template<typename Key, int FlatSize>
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bool PDFFlatMap<Key, FlatSize>::empty() const
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{
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return size() == 0;
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}
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} // namespace pdf
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#endif // PDFFLATMAP_H
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