/*
 * Tiny Vector Matrix Library
 * Dense Vector Matrix Libary of Tiny size using Expression Templates
 *
 * Copyright (C) 2001 - 2007 Olaf Petzold <opetzold@users.sourceforge.net>
 *
 * This library 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 2.1 of the License, or (at your option) any later version.
 *
 * This library 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 this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * $Id: Gemm.h,v 1.12 2007-06-23 15:58:59 opetzold Exp $
 */

#ifndef TVMET_LOOP_GEMM_H
#define TVMET_LOOP_GEMM_H

namespace tvmet {

namespace loop {


/**
 * \class gemm Gemm.h "tvmet/loop/Gemm.h"
 * \brief class for matrix-matrix product using loop unrolling.
 *        using formula
 *        \f[
 *        M_1\,M_2
 *        \f]
 * \par Example:
 * \code
 * template<class T, std::size_t Rows1, std::size_t Cols1, std::size_t Cols2>
 * inline
 * void
 * prod(const Matrix<T, Rows1, Cols1>& lhs, const Matrix<T, Cols1, Cols2>& rhs,
 *     Matrix<T, Rows1, Cols2>& dest)
 * {
 *   for (std::size_t i = 0; i != Rows1; ++i) {
 *     for (std::size_t j = 0; j != Cols2; ++j) {
 *       dest(i, j) = tvmet::loop::gemm<Rows1, Cols1, Cols2>().prod(lhs, rhs, i, j);
 *     }
 *   }
 * }
 * \endcode
 * \note The number of rows of rhs matrix have to be equal to cols of lhs matrix.
 *       The result is a (Rows1 x Cols2) matrix.
 */
template<std::size_t Rows1, std::size_t Cols1,
     std::size_t Cols2>
class gemm
{
  gemm(const gemm&);
  gemm& operator=(const gemm&);

private:
  enum {
    count     = Cols1,
    N         = (count+7)/8
  };

public:
  gemm() { }

public:
  template<class E1, class E2>
  static inline
  typename PromoteTraits<
    typename E1::value_type,
    typename E2::value_type
    >::value_type
  prod(const E1& lhs, const E2& rhs, std::size_t i, std::size_t j) {
    typename PromoteTraits<
      typename E1::value_type,
      typename E2::value_type
    >::value_type                  sum(0);
    std::size_t                 k(0);
    std::size_t                 n(N);

    // Duff's device
    switch(count % 8) {
    case 0: do { sum += lhs(i, k) * rhs(k, j); ++k;
    case 7:      sum += lhs(i, k) * rhs(k, j); ++k;
    case 6:      sum += lhs(i, k) * rhs(k, j); ++k;
    case 5:      sum += lhs(i, k) * rhs(k, j); ++k;
    case 4:      sum += lhs(i, k) * rhs(k, j); ++k;
    case 3:      sum += lhs(i, k) * rhs(k, j); ++k;
    case 2:      sum += lhs(i, k) * rhs(k, j); ++k;
    case 1:      sum += lhs(i, k) * rhs(k, j); ++k;
            } while(--n != 0);
    }

    return sum;
  }
};


} // namespace loop

} // namespace tvmet

#endif /* TVMET_LOOP_GEMM_H */

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