Tpetra_Details_defaultGemm.hpp

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#ifndef TPETRA_DETAILS_DEFAULTGEMM_HPP
#define TPETRA_DETAILS_DEFAULTGEMM_HPP


#include "TpetraCore_config.h"
#include "Kokkos_ArithTraits.hpp"
#include "Kokkos_Complex.hpp"
#include <type_traits>

namespace Tpetra {
namespace Details {
namespace Blas {
namespace Default {

template<class ViewType1,
         class ViewType2,
         class ViewType3,
         class CoefficientType,
         class IndexType = int>
void
gemm (const char transA,
      const char transB,
      const CoefficientType& alpha,
      const ViewType1& A,
      const ViewType2& B,
      const CoefficientType& beta,
      const ViewType3& C)
{
  // Assert that A, B, and C are in fact matrices
  static_assert (ViewType1::rank == 2, "GEMM: A must have rank 2 (be a matrix).");
  static_assert (ViewType2::rank == 2, "GEMM: B must have rank 2 (be a matrix).");
  static_assert (ViewType3::rank == 2, "GEMM: C must have rank 2 (be a matrix).");

  typedef typename ViewType3::non_const_value_type c_value_type;
  typedef Kokkos::Details::ArithTraits<CoefficientType> STS;
  const CoefficientType ZERO = STS::zero ();
  const CoefficientType ONE = STS::one ();

  // Get the dimensions
  IndexType m, n, k;
  if (transA == 'N' || transA == 'n') {
    m = static_cast<IndexType> (A.dimension_0 ());
    n = static_cast<IndexType> (A.dimension_1 ());
  }
  else {
    m = static_cast<IndexType> (A.dimension_1 ());
    n = static_cast<IndexType> (A.dimension_0 ());
  }
  k = static_cast<IndexType> (C.dimension_1 ());

  // quick return if possible
  if (alpha == ZERO && beta == ONE) {
    return;
  }

  // And if alpha equals zero...
  if (alpha == ZERO) {
    if (beta == ZERO) {
      for (IndexType i = 0; i < m; ++i) {
        for (IndexType j = 0; j < k; ++j) {
          C(i,j) = ZERO;
        }
      }
    }
    else {
      for (IndexType i = 0; i < m; ++i) {
        for (IndexType j = 0; j < k; ++j) {
          C(i,j) = beta*C(i,j);
        }
      }
    }
  }

  // Start the operations
  if (transB == 'n' || transB == 'N') {
    if (transA == 'n' || transA == 'N') {
      // Form C = alpha*A*B + beta*C
      for (IndexType j = 0; j < n; ++j) {
        if (beta == ZERO) {
          for (IndexType i = 0; i < m; ++i) {
            C(i,j) = ZERO;
          }
        }
        else if (beta != ONE) {
          for (IndexType i = 0; i < m; ++i) {
            C(i,j) = beta*C(i,j);
          }
        }
        for (IndexType l = 0; l < k; ++l) {
          // Don't use c_value_type here, since it unnecessarily
          // forces type conversion before we assign to C(i,j).
          auto temp = alpha*B(l,j);
          for (IndexType i = 0; i < m; ++i) {
            C(i,j) = C(i,j) + temp*A(i,l);
          }
        }
      }
    }
    else {
      // Form C = alpha*A**T*B + beta*C
      for (IndexType j = 0; j < n; ++j) {
        for (IndexType i = 0; i < m; ++i) {
          c_value_type temp = ZERO;
          for (IndexType l = 0; l < k; ++l) {
            temp = temp + A(l,i)*B(l,j);
          }
          if (beta == ZERO) {
            C(i,j) = alpha*temp;
          }
          else {
            C(i,j) = alpha*temp + beta*C(i,j);
          }
        }
      }
    }
  }
  else {
    if (transA == 'n' || transA == 'N') {
      // Form C = alpha*A*B**T + beta*C
      for (IndexType j = 0; j < n; ++j) {
        if (beta == ZERO) {
          for (IndexType i = 0; i < m; ++i) {
            C(i,j) = ZERO;
          }
        }
        else if (beta != ONE) {
          for (IndexType i = 0; i < m; ++i) {
            C(i,j) = beta*C(i,j);
          }
        }
        for (IndexType l = 0; l < k; ++l) {
          // Don't use c_value_type here, since it unnecessarily
          // forces type conversion before we assign to C(i,j).
          auto temp = alpha*B(j,l);
          for (IndexType i = 0; i < m; ++i) {
            C(i,j) = C(i,j) + temp*A(i,l);
          }
        }
      }
    }
    else {
      // Form C = alpha*A**T*B**T + beta*C
      for (IndexType j = 0; j < n; ++j) {
        for (IndexType i = 0; i < m; ++i) {
          c_value_type temp = ZERO;
          for (IndexType l = 0; l < k; ++l) {
            temp = temp + A(l,i)*B(j,l);
          }
          if (beta == ZERO) {
            C(i,j) = alpha*temp;
          }
          else {
            C(i,j) = alpha*temp + beta*C(i,j);
          }
        }
      }
    }
  }
}

} // namespace Default
} // namespace Blas
} // namespace Details
} // namespace Tpetra

#endif // TPETRA_DETAILS_DEFAULTGEMM_HPP