eigen/Eigen/src/Core/Ref.h

// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2012 Gael Guennebaud <gael.guennebaud@inria.fr>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

#ifndef EIGEN_REF_H
#define EIGEN_REF_H

// IWYU pragma: private
#include "./InternalHeaderCheck.h"

namespace Eigen {

namespace internal {

template <typename PlainObjectType_, int Options_, typename StrideType_>
struct traits<Ref<PlainObjectType_, Options_, StrideType_> >
    : public traits<Map<PlainObjectType_, Options_, StrideType_> > {
  typedef PlainObjectType_ PlainObjectType;
  typedef StrideType_ StrideType;
  enum {
    Options = Options_,
    Flags = traits<Map<PlainObjectType_, Options_, StrideType_> >::Flags | NestByRefBit,
    Alignment = traits<Map<PlainObjectType_, Options_, StrideType_> >::Alignment,
    InnerStrideAtCompileTime = traits<Map<PlainObjectType_, Options_, StrideType_> >::InnerStrideAtCompileTime,
    OuterStrideAtCompileTime = traits<Map<PlainObjectType_, Options_, StrideType_> >::OuterStrideAtCompileTime
  };

  template <typename Derived>
  struct match {
    enum {
      IsVectorAtCompileTime = PlainObjectType::IsVectorAtCompileTime || Derived::IsVectorAtCompileTime,
      HasDirectAccess = internal::has_direct_access<Derived>::ret,
      StorageOrderMatch =
          IsVectorAtCompileTime || ((PlainObjectType::Flags & RowMajorBit) == (Derived::Flags & RowMajorBit)),
      InnerStrideMatch = int(InnerStrideAtCompileTime) == int(Dynamic) ||
                         int(InnerStrideAtCompileTime) == int(Derived::InnerStrideAtCompileTime) ||
                         (int(InnerStrideAtCompileTime) == 0 && int(Derived::InnerStrideAtCompileTime) == 1),
      OuterStrideMatch = IsVectorAtCompileTime || int(OuterStrideAtCompileTime) == int(Dynamic) ||
                         int(OuterStrideAtCompileTime) == int(Derived::OuterStrideAtCompileTime),
      // NOTE, this indirection of evaluator<Derived>::Alignment is needed
      // to workaround a very strange bug in MSVC related to the instantiation
      // of has_*ary_operator in evaluator<CwiseNullaryOp>.
      // This line is surprisingly very sensitive. For instance, simply adding parenthesis
      // as "DerivedAlignment = (int(evaluator<Derived>::Alignment))," will make MSVC fail...
      DerivedAlignment = int(evaluator<Derived>::Alignment),
      AlignmentMatch = (int(traits<PlainObjectType>::Alignment) == int(Unaligned)) ||
                       (DerivedAlignment >= int(Alignment)),  // FIXME the first condition is not very clear, it should
                                                              // be replaced by the required alignment
      ScalarTypeMatch = internal::is_same<typename PlainObjectType::Scalar, typename Derived::Scalar>::value,
      MatchAtCompileTime = HasDirectAccess && StorageOrderMatch && InnerStrideMatch && OuterStrideMatch &&
                           AlignmentMatch && ScalarTypeMatch
    };
    typedef std::conditional_t<MatchAtCompileTime, internal::true_type, internal::false_type> type;
  };
};

template <typename Derived>
struct traits<RefBase<Derived> > : public traits<Derived> {};

}  // namespace internal

template <typename Derived>
class RefBase : public MapBase<Derived> {
  typedef typename internal::traits<Derived>::PlainObjectType PlainObjectType;
  typedef typename internal::traits<Derived>::StrideType StrideType;

 public:
  typedef MapBase<Derived> Base;
  EIGEN_DENSE_PUBLIC_INTERFACE(RefBase)

  EIGEN_DEVICE_FUNC constexpr Index innerStride() const {
    return StrideType::InnerStrideAtCompileTime != 0 ? m_stride.inner() : 1;
  }

  EIGEN_DEVICE_FUNC constexpr Index outerStride() const {
    return StrideType::OuterStrideAtCompileTime != 0 ? m_stride.outer()
           : IsVectorAtCompileTime                   ? this->size()
           : int(Flags) & RowMajorBit                ? this->cols()
                                                     : this->rows();
  }

  EIGEN_DEVICE_FUNC RefBase()
      : Base(0, RowsAtCompileTime == Dynamic ? 0 : RowsAtCompileTime,
             ColsAtCompileTime == Dynamic ? 0 : ColsAtCompileTime),
        // Stride<> does not allow default ctor for Dynamic strides, so let' initialize it with dummy values:
        m_stride(StrideType::OuterStrideAtCompileTime == Dynamic ? 0 : StrideType::OuterStrideAtCompileTime,
                 StrideType::InnerStrideAtCompileTime == Dynamic ? 0 : StrideType::InnerStrideAtCompileTime) {}

  EIGEN_INHERIT_ASSIGNMENT_OPERATORS(RefBase)

 protected:
  typedef Stride<StrideType::OuterStrideAtCompileTime, StrideType::InnerStrideAtCompileTime> StrideBase;

  // Resolves inner stride if default 0.
  static EIGEN_DEVICE_FUNC constexpr Index resolveInnerStride(Index inner) { return inner == 0 ? 1 : inner; }

  // Resolves outer stride if default 0.
  static EIGEN_DEVICE_FUNC constexpr Index resolveOuterStride(Index inner, Index outer, Index rows, Index cols,
                                                              bool isVectorAtCompileTime, bool isRowMajor) {
    return outer == 0 ? isVectorAtCompileTime ? inner * rows * cols : isRowMajor ? inner * cols : inner * rows : outer;
  }

  // Returns true if construction is valid, false if there is a stride mismatch,
  // and fails if there is a size mismatch.
  template <typename Expression>
  EIGEN_DEVICE_FUNC bool construct(Expression& expr) {
    // Check matrix sizes.  If this is a compile-time vector, we do allow
    // implicitly transposing.
    EIGEN_STATIC_ASSERT(EIGEN_PREDICATE_SAME_MATRIX_SIZE(PlainObjectType, Expression)
                            // If it is a vector, the transpose sizes might match.
                            || (PlainObjectType::IsVectorAtCompileTime &&
                                ((int(PlainObjectType::RowsAtCompileTime) == Eigen::Dynamic ||
                                  int(Expression::ColsAtCompileTime) == Eigen::Dynamic ||
                                  int(PlainObjectType::RowsAtCompileTime) == int(Expression::ColsAtCompileTime)) &&
                                 (int(PlainObjectType::ColsAtCompileTime) == Eigen::Dynamic ||
                                  int(Expression::RowsAtCompileTime) == Eigen::Dynamic ||
                                  int(PlainObjectType::ColsAtCompileTime) == int(Expression::RowsAtCompileTime)))),
                        YOU_MIXED_MATRICES_OF_DIFFERENT_SIZES)

    // Determine runtime rows and columns.
    Index rows = expr.rows();
    Index cols = expr.cols();
    if (PlainObjectType::RowsAtCompileTime == 1) {
      eigen_assert(expr.rows() == 1 || expr.cols() == 1);
      rows = 1;
      cols = expr.size();
    } else if (PlainObjectType::ColsAtCompileTime == 1) {
      eigen_assert(expr.rows() == 1 || expr.cols() == 1);
      rows = expr.size();
      cols = 1;
    }
    // Verify that the sizes are valid.
    eigen_assert((PlainObjectType::RowsAtCompileTime == Dynamic) || (PlainObjectType::RowsAtCompileTime == rows));
    eigen_assert((PlainObjectType::ColsAtCompileTime == Dynamic) || (PlainObjectType::ColsAtCompileTime == cols));

    // If this is a vector, we might be transposing, which means that stride should swap.
    const bool transpose = PlainObjectType::IsVectorAtCompileTime && (rows != expr.rows());
    // If the storage format differs, we also need to swap the stride.
    const bool row_major = ((PlainObjectType::Flags)&RowMajorBit) != 0;
    const bool expr_row_major = (Expression::Flags & RowMajorBit) != 0;
    const bool storage_differs = (row_major != expr_row_major);

    const bool swap_stride = (transpose != storage_differs);

    // Determine expr's actual strides, resolving any defaults if zero.
    const Index expr_inner_actual = resolveInnerStride(expr.innerStride());
    const Index expr_outer_actual = resolveOuterStride(expr_inner_actual, expr.outerStride(), expr.rows(), expr.cols(),
                                                       Expression::IsVectorAtCompileTime != 0, expr_row_major);

    // If this is a column-major row vector or row-major column vector, the inner-stride
    // is arbitrary, so set it to either the compile-time inner stride or 1.
    const bool row_vector = (rows == 1);
    const bool col_vector = (cols == 1);
    const Index inner_stride =
        ((!row_major && row_vector) || (row_major && col_vector))
            ? (StrideType::InnerStrideAtCompileTime > 0 ? Index(StrideType::InnerStrideAtCompileTime) : 1)
        : swap_stride ? expr_outer_actual
                      : expr_inner_actual;

    // If this is a column-major column vector or row-major row vector, the outer-stride
    // is arbitrary, so set it to either the compile-time outer stride or vector size.
    const Index outer_stride =
        ((!row_major && col_vector) || (row_major && row_vector))
            ? (StrideType::OuterStrideAtCompileTime > 0 ? Index(StrideType::OuterStrideAtCompileTime)
                                                        : rows * cols * inner_stride)
        : swap_stride ? expr_inner_actual
                      : expr_outer_actual;

    // Check if given inner/outer strides are compatible with compile-time strides.
    const bool inner_valid = (StrideType::InnerStrideAtCompileTime == Dynamic) ||
                             (resolveInnerStride(Index(StrideType::InnerStrideAtCompileTime)) == inner_stride);
    if (!inner_valid) {
      return false;
    }

    const bool outer_valid =
        (StrideType::OuterStrideAtCompileTime == Dynamic) ||
        (resolveOuterStride(inner_stride, Index(StrideType::OuterStrideAtCompileTime), rows, cols,
                            PlainObjectType::IsVectorAtCompileTime != 0, row_major) == outer_stride);
    if (!outer_valid) {
      return false;
    }

    internal::construct_at<Base>(this, expr.data(), rows, cols);
    internal::construct_at(&m_stride, (StrideType::OuterStrideAtCompileTime == 0) ? 0 : outer_stride,
                           (StrideType::InnerStrideAtCompileTime == 0) ? 0 : inner_stride);
    return true;
  }

  StrideBase m_stride;
};

/** \class Ref
 * \ingroup Core_Module
 *
 * \brief A matrix or vector expression mapping an existing expression
 *
 * \tparam PlainObjectType the equivalent matrix type of the mapped data
 * \tparam Options specifies the pointer alignment in bytes. It can be: \c #Aligned128, , \c #Aligned64, \c #Aligned32,
 * \c #Aligned16, \c #Aligned8 or \c #Unaligned. The default is \c #Unaligned. \tparam StrideType optionally specifies
 * strides. By default, Ref implies a contiguous storage along the inner dimension (inner stride==1), but accepts a
 * variable outer stride (leading dimension). This can be overridden by specifying strides. The type passed here must be
 * a specialization of the Stride template, see examples below.
 *
 * This class provides a way to write non-template functions taking Eigen objects as parameters while limiting the
 * number of copies. A Ref<> object can represent either a const expression or a l-value: \code
 * // in-out argument:
 * void foo1(Ref<VectorXf> x);
 *
 * // read-only const argument:
 * void foo2(const Ref<const VectorXf>& x);
 * \endcode
 *
 * In the in-out case, the input argument must satisfy the constraints of the actual Ref<> type, otherwise a compilation
 * issue will be triggered. By default, a Ref<VectorXf> can reference any dense vector expression of float having a
 * contiguous memory layout. Likewise, a Ref<MatrixXf> can reference any column-major dense matrix expression of float
 * whose column's elements are contiguously stored with the possibility to have a constant space in-between each column,
 * i.e. the inner stride must be equal to 1, but the outer stride (or leading dimension) can be greater than the number
 * of rows.
 *
 * In the const case, if the input expression does not match the above requirement, then it is evaluated into a
 * temporary before being passed to the function. Here are some examples: \code MatrixXf A; VectorXf a; foo1(a.head());
 * // OK foo1(A.col());              // OK foo1(A.row());              // Compilation error because here innerstride!=1
 * foo2(A.row());              // Compilation error because A.row() is a 1xN object while foo2 is expecting a Nx1 object
 * foo2(A.row().transpose());  // The row is copied into a contiguous temporary
 * foo2(2*a);                  // The expression is evaluated into a temporary
 * foo2(A.col().segment(2,4)); // No temporary
 * \endcode
 *
 * The range of inputs that can be referenced without temporary can be enlarged using the last two template parameters.
 * Here is an example accepting an innerstride!=1:
 * \code
 * // in-out argument:
 * void foo3(Ref<VectorXf,0,InnerStride<> > x);
 * foo3(A.row());              // OK
 * \endcode
 * The downside here is that the function foo3 might be significantly slower than foo1 because it won't be able to
 * exploit vectorization, and will involve more expensive address computations even if the input is contiguously stored
 * in memory. To overcome this issue, one might propose to overload internally calling a template function, e.g.: \code
 * // in the .h:
 * void foo(const Ref<MatrixXf>& A);
 * void foo(const Ref<MatrixXf,0,Stride<> >& A);
 *
 * // in the .cpp:
 * template<typename TypeOfA> void foo_impl(const TypeOfA& A) {
 *     ... // crazy code goes here
 * }
 * void foo(const Ref<MatrixXf>& A) { foo_impl(A); }
 * void foo(const Ref<MatrixXf,0,Stride<> >& A) { foo_impl(A); }
 * \endcode
 *
 * See also the following stackoverflow questions for further references:
 *  - <a href="http://stackoverflow.com/questions/21132538/correct-usage-of-the-eigenref-class">Correct usage of the
 * Eigen::Ref<> class</a>
 *
 * \sa PlainObjectBase::Map(), \ref TopicStorageOrders
 */
template <typename PlainObjectType, int Options, typename StrideType>
class Ref : public RefBase<Ref<PlainObjectType, Options, StrideType> > {
 private:
  typedef internal::traits<Ref> Traits;
  template <typename Derived>
  EIGEN_DEVICE_FUNC inline Ref(
      const PlainObjectBase<Derived>& expr,
      std::enable_if_t<bool(Traits::template match<Derived>::MatchAtCompileTime), Derived>* = 0);

 public:
  typedef RefBase<Ref> Base;
  EIGEN_DENSE_PUBLIC_INTERFACE(Ref)

#ifndef EIGEN_PARSED_BY_DOXYGEN
  template <typename Derived>
  EIGEN_DEVICE_FUNC inline Ref(
      PlainObjectBase<Derived>& expr,
      std::enable_if_t<bool(Traits::template match<Derived>::MatchAtCompileTime), Derived>* = 0) {
    EIGEN_STATIC_ASSERT(bool(Traits::template match<Derived>::MatchAtCompileTime), STORAGE_LAYOUT_DOES_NOT_MATCH);
    // Construction must pass since we will not create temporary storage in the non-const case.
    const bool success = Base::construct(expr.derived());
    EIGEN_UNUSED_VARIABLE(success)
    eigen_assert(success);
  }
  template <typename Derived>
  EIGEN_DEVICE_FUNC inline Ref(
      const DenseBase<Derived>& expr,
      std::enable_if_t<bool(Traits::template match<Derived>::MatchAtCompileTime), Derived>* = 0)
#else
  /** Implicit constructor from any dense expression */
  template <typename Derived>
  inline Ref(DenseBase<Derived>& expr)
#endif
  {
    EIGEN_STATIC_ASSERT(bool(internal::is_lvalue<Derived>::value), THIS_EXPRESSION_IS_NOT_A_LVALUE__IT_IS_READ_ONLY);
    EIGEN_STATIC_ASSERT(bool(Traits::template match<Derived>::MatchAtCompileTime), STORAGE_LAYOUT_DOES_NOT_MATCH);
    EIGEN_STATIC_ASSERT(!Derived::IsPlainObjectBase, THIS_EXPRESSION_IS_NOT_A_LVALUE__IT_IS_READ_ONLY);
    // Construction must pass since we will not create temporary storage in the non-const case.
    const bool success = Base::construct(expr.const_cast_derived());
    EIGEN_UNUSED_VARIABLE(success)
    eigen_assert(success);
  }

  EIGEN_INHERIT_ASSIGNMENT_OPERATORS(Ref)
};

// this is the const ref version
template <typename TPlainObjectType, int Options, typename StrideType>
class Ref<const TPlainObjectType, Options, StrideType>
    : public RefBase<Ref<const TPlainObjectType, Options, StrideType> > {
  typedef internal::traits<Ref> Traits;

  static constexpr bool may_map_m_object_successfully =
      (static_cast<int>(StrideType::InnerStrideAtCompileTime) == 0 ||
       static_cast<int>(StrideType::InnerStrideAtCompileTime) == 1 ||
       static_cast<int>(StrideType::InnerStrideAtCompileTime) == Dynamic) &&
      (TPlainObjectType::IsVectorAtCompileTime || static_cast<int>(StrideType::OuterStrideAtCompileTime) == 0 ||
       static_cast<int>(StrideType::OuterStrideAtCompileTime) == Dynamic ||
       static_cast<int>(StrideType::OuterStrideAtCompileTime) ==
           static_cast<int>(TPlainObjectType::InnerSizeAtCompileTime) ||
       static_cast<int>(TPlainObjectType::InnerSizeAtCompileTime) == Dynamic);

 public:
  typedef RefBase<Ref> Base;
  EIGEN_DENSE_PUBLIC_INTERFACE(Ref)

  template <typename Derived>
  EIGEN_DEVICE_FUNC inline Ref(const DenseBase<Derived>& expr,
                               std::enable_if_t<bool(Traits::template match<Derived>::ScalarTypeMatch), Derived>* = 0) {
    //      std::cout << match_helper<Derived>::HasDirectAccess << "," << match_helper<Derived>::OuterStrideMatch << ","
    //      << match_helper<Derived>::InnerStrideMatch << "\n"; std::cout << int(StrideType::OuterStrideAtCompileTime)
    //      << " - " << int(Derived::OuterStrideAtCompileTime) << "\n"; std::cout <<
    //      int(StrideType::InnerStrideAtCompileTime) << " - " << int(Derived::InnerStrideAtCompileTime) << "\n";
    EIGEN_STATIC_ASSERT(Traits::template match<Derived>::type::value || may_map_m_object_successfully,
                        STORAGE_LAYOUT_DOES_NOT_MATCH);
    construct(expr.derived(), typename Traits::template match<Derived>::type());
  }

  EIGEN_DEVICE_FUNC inline Ref(const Ref& other) : Base(other) {
    // copy constructor shall not copy the m_object, to avoid unnecessary malloc and copy
  }

  EIGEN_DEVICE_FUNC inline Ref(Ref&& other) {
    if (other.data() == other.m_object.data()) {
      m_object = std::move(other.m_object);
      Base::construct(m_object);
    } else
      Base::construct(other);
  }

  template <typename OtherRef>
  EIGEN_DEVICE_FUNC inline Ref(const RefBase<OtherRef>& other) {
    EIGEN_STATIC_ASSERT(Traits::template match<OtherRef>::type::value || may_map_m_object_successfully,
                        STORAGE_LAYOUT_DOES_NOT_MATCH);
    construct(other.derived(), typename Traits::template match<OtherRef>::type());
  }

 protected:
  template <typename Expression>
  EIGEN_DEVICE_FUNC void construct(const Expression& expr, internal::true_type) {
    // Check if we can use the underlying expr's storage directly, otherwise call the copy version.
    if (!Base::construct(expr)) {
      construct(expr, internal::false_type());
    }
  }

  template <typename Expression>
  EIGEN_DEVICE_FUNC void construct(const Expression& expr, internal::false_type) {
    internal::call_assignment_no_alias(m_object, expr, internal::assign_op<Scalar, Scalar>());
    const bool success = Base::construct(m_object);
    EIGEN_ONLY_USED_FOR_DEBUG(success)
    eigen_assert(success);
  }

 protected:
  TPlainObjectType m_object;
};

}  // end namespace Eigen

#endif  // EIGEN_REF_H