Issue #118: First part of splitting

Pdf4QtLibCore/sources/pdfflatmap.h

@@ -0,0 +1,130 @@
+//    Copyright (C) 2018-2021 Jakub Melka
+//
+//    This file is part of PDF4QT.
+//
+//    PDF4QT 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
+//    with the written consent of the copyright owner, any later version.
+//
+//    PDF4QT 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 PDF4QT.  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