Patch by Gael Guennebaud:

Rework the matrix storage to ensure optimal sizeof in all cases, while
keeping the decoupling of matrix sizes versus storage sizes.
Also fixing (recently introduced) bugs caused by unwanted
reallocations of the buffers.

Eigen/src/Core/MatrixStorage.h

@@ -0,0 +1,184 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra. Eigen itself is part of the KDE project.
+//
+// Copyright (C) 2008 Gael Guennebaud <gael.guennebaud@gmail.com>
+// Copyright (C) 2006-2008 Benoit Jacob <jacob@math.jussieu.fr>
+//
+// Eigen 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.
+//
+// Alternatively, you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of 
+// the License, or (at your option) any later version.
+//
+// Eigen 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 or the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public 
+// License and a copy of the GNU General Public License along with
+// Eigen. If not, see <http://www.gnu.org/licenses/>.
+
+#ifndef EIGEN_MATRIXSTORAGE_H
+#define EIGEN_MATRIXSTORAGE_H
+
+
+/** \class MatrixStorage
+  *
+  * \brief Stores the data of a matrix
+  *
+  * \internal
+  *
+  * This class stores the data of fixed-size, dynamic-size or mixed matrices
+  * in a way as compact as possible.
+  *
+  * \sa Matrix
+  */
+template<typename T, int Size, int _Rows, int _Cols> class MatrixStorage;
+
+// purely fixed-size matrix.
+template<typename T, int Size, int _Rows, int _Cols> class MatrixStorage
+{
+    T m_data[Size];
+  public:
+    MatrixStorage() {}
+    MatrixStorage(int,int,int) {}
+    static int rows(void) {return _Rows;}
+    static int cols(void) {return _Cols;}
+    void resize(int,int,int) {}
+    const T *data() const { return m_data; }
+    T *data() { return m_data; }
+};
+
+// dynamic-size matrix with fixed-size storage
+template<typename T, int Size> class MatrixStorage<T, Size, Dynamic, Dynamic>
+{
+    T m_data[Size];
+    int m_rows;
+    int m_cols;
+  public:
+    MatrixStorage(int, int nbRows, int nbCols) : m_rows(nbRows), m_cols(nbCols) {}
+    ~MatrixStorage() {}
+    int rows(void) const {return m_rows;}
+    int cols(void) const {return m_cols;}
+    void resize(int, int nbRows, int nbCols)
+    {
+      m_rows = nbRows;
+      m_cols = nbCols;
+    }
+    const T *data() const { return m_data; }
+    T *data() { return m_data; }
+};
+
+// dynamic-size matrix with fixed-size storage and fixed width
+template<typename T, int Size, int _Cols> class MatrixStorage<T, Size, Dynamic, _Cols>
+{
+    T m_data[Size];
+    int m_rows;
+  public:
+    MatrixStorage(int, int nbRows, int) : m_rows(nbRows) {}
+    ~MatrixStorage() {}
+    int rows(void) const {return m_rows;}
+    int cols(void) const {return _Cols;}
+    void resize(int size, int nbRows, int)
+    {
+      m_rows = nbRows;
+    }
+    const T *data() const { return m_data; }
+    T *data() { return m_data; }
+};
+
+// dynamic-size matrix with fixed-size storage and fixed height
+template<typename T, int Size, int _Rows> class MatrixStorage<T, Size, _Rows, Dynamic>
+{
+    T m_data[Size];
+    int m_cols;
+  public:
+    MatrixStorage(int, int nbRows, int nbCols) : m_cols(nbCols) {}
+    ~MatrixStorage() {}
+    int rows(void) const {return _Rows;}
+    int cols(void) const {return m_cols;}
+    void resize(int size, int, int nbCols)
+    {
+      m_cols = nbCols;
+    }
+    const T *data() const { return m_data; }
+    T *data() { return m_data; }
+};
+
+// purely dynamic matrix.
+template<typename T> class MatrixStorage<T, Dynamic, Dynamic, Dynamic>
+{
+    T *m_data;
+    int m_rows;
+    int m_cols;
+  public:
+    MatrixStorage(int size, int nbRows, int nbCols) : m_data(new T[size]), m_rows(nbRows), m_cols(nbCols) {}
+    ~MatrixStorage() { delete[] m_data; }
+    int rows(void) const {return m_rows;}
+    int cols(void) const {return m_cols;}
+    void resize(int size, int nbRows, int nbCols)
+    {
+      if(size != m_rows*m_cols)
+      {
+        delete[] m_data;
+        m_data = new T[size];
+      }
+      m_rows = nbRows;
+      m_cols = nbCols;
+    }
+    const T *data() const { return m_data; }
+    T *data() { return m_data; }
+};
+
+// matrix with dynamic width and fixed height (so that matrix has dynamic size).
+template<typename T, int _Rows> class MatrixStorage<T, Dynamic, _Rows, Dynamic>
+{
+    T *m_data;
+    int m_cols;
+  public:
+    MatrixStorage(int size, int, int nbCols) : m_data(new T[size]), m_cols(nbCols) {}
+    ~MatrixStorage() { delete[] m_data; }
+    static int rows(void) {return _Rows;}
+    int cols(void) const {return m_cols;}
+    void resize(int size, int, int nbCols)
+    {
+      if(size != _Rows*m_cols)
+      {
+        delete[] m_data;
+        m_data = new T[size];
+      }
+      m_cols = nbCols;
+    }
+    const T *data() const { return m_data; }
+    T *data() { return m_data; }
+};
+
+// matrix with dynamic height and fixed width (so that matrix has dynamic size).
+template<typename T, int _Cols> class MatrixStorage<T, Dynamic, Dynamic, _Cols>
+{
+    T *m_data;
+    int m_rows;
+  public:
+    MatrixStorage(int size, int nbRows, int) : m_data(new T[size]), m_rows(nbRows) {}
+    ~MatrixStorage() { delete[] m_data; }
+    int rows(void) const {return m_rows;}
+    static int cols(void) {return _Cols;}
+    void resize(int size, int nbRows, int)
+    {
+      if(size != m_rows*_Cols)
+      {
+        delete[] m_data;
+        m_data = new T[size];
+      }
+      m_rows = nbRows;
+    }
+    const T *data() const { return m_data; }
+    T *data() { return m_data; }
+};
+
+#endif // EIGEN_MATRIX_H