PDF4QT/PdfForQtLib/sources/pdfflatmap.h

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2019-07-01 12:35:53 +02:00
// Copyright (C) 2018-2019 Jakub Melka
//
// This file is part of PdfForQt.
//
// PdfForQt is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// PdfForQt is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with PDFForQt. If not, see <https://www.gnu.org/licenses/>.
#ifndef PDFFLATMAP_H
#define PDFFLATMAP_H
#include <set>
#include <array>
#include <algorithm>
namespace pdf
{
/// This class behaves like std::set, but have "flat" part, and if size of the set
/// is small (smaller than \p FlatSize), then no memory allocation is needed. This
/// container supports inserting, deleting and searching for the object presence.
template<typename Key, int FlatSize>
class PDFFlatMap
{
public:
constexpr inline PDFFlatMap();
/// Inserts a key in the container. Checks, if key is already present
/// in the container, in this case no insertion occurs.
/// \param key Key to be inserted
void insert(const Key& key);
/// Erases a key in the container, if it is in the set
/// \param key Key to be erased
void erase(const Key& key);
/// Searchs for a given key. If it is found, true is returned, false otherwise.
/// \param key Key to be searched
bool search(const Key& key) const;
/// Returns size of the container
std::size_t size() const;
/// Returns true, if container is empty
bool empty() const;
private:
/// Flat part of the set
std::array<Key, FlatSize> m_flat;
/// This iterator points to first empty position, or it is
/// the last iterator (pointing to the end of the array).
typename std::array<Key, FlatSize>::iterator m_flatEmptyPosition;
std::set<Key> m_overflowContainer;
};
template<typename Key, int FlatSize>
constexpr PDFFlatMap<Key, FlatSize>::PDFFlatMap() :
m_flat(),
m_flatEmptyPosition(m_flat.begin()),
m_overflowContainer()
{
}
template<typename Key, int FlatSize>
void PDFFlatMap<Key, FlatSize>::insert(const Key& key)
{
if (!search(key))
{
// Try to insert key in the flat part, if possible (we are not at end of the array)
if (m_flatEmptyPosition != m_flat.end())
{
*m_flatEmptyPosition++ = key;
}
else
{
m_overflowContainer.insert(key);
}
}
}
template<typename Key, int FlatSize>
void PDFFlatMap<Key, FlatSize>::erase(const Key& key)
{
// First we must check, if the key is present in the flat part. If yes, then remove key
// from the flat part and try to move one item from the overflow part to the flat part, if possible.
// Otherwise check overflow part.
m_flatEmptyPosition = std::remove_if(m_flat.begin(), m_flatEmptyPosition, [&key](const Key& otherKey) { return key == otherKey; });
m_overflowContainer.erase(key);
if (!m_overflowContainer.empty() && m_flatEmptyPosition != m_flat.end())
{
*m_flatEmptyPosition++ = *m_overflowContainer.begin();
m_overflowContainer.erase(m_overflowContainer.begin());
}
}
template<typename Key, int FlatSize>
bool PDFFlatMap<Key, FlatSize>::search(const Key& key) const
{
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));
}
template<typename Key, int FlatSize>
std::size_t PDFFlatMap<Key, FlatSize>::size() const
{
return std::distance<typename std::array<Key, FlatSize>::const_iterator>(m_flat.begin(), m_flatEmptyPosition) + m_overflowContainer.size();
}
template<typename Key, int FlatSize>
bool PDFFlatMap<Key, FlatSize>::empty() const
{
return size() == 0;
}
} // namespace pdf
#endif // PDFFLATMAP_H