eigen/Eigen/src/Core/Map.h

// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2007-2010 Benoit Jacob <jacob.benoit.1@gmail.com>
// Copyright (C) 2008 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_MAP_H
#define EIGEN_MAP_H

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

namespace Eigen {

namespace internal {
template <typename PlainObjectType, int MapOptions, typename StrideType>
struct traits<Map<PlainObjectType, MapOptions, StrideType> > : public traits<PlainObjectType> {
  typedef traits<PlainObjectType> TraitsBase;
  enum {
    PlainObjectTypeInnerSize = ((traits<PlainObjectType>::Flags & RowMajorBit) == RowMajorBit)
                                   ? PlainObjectType::ColsAtCompileTime
                                   : PlainObjectType::RowsAtCompileTime,

    InnerStrideAtCompileTime = StrideType::InnerStrideAtCompileTime == 0
                                   ? int(PlainObjectType::InnerStrideAtCompileTime)
                                   : int(StrideType::InnerStrideAtCompileTime),
    OuterStrideAtCompileTime = StrideType::OuterStrideAtCompileTime == 0
                                   ? (InnerStrideAtCompileTime == Dynamic || PlainObjectTypeInnerSize == Dynamic
                                          ? Dynamic
                                          : int(InnerStrideAtCompileTime) * int(PlainObjectTypeInnerSize))
                                   : int(StrideType::OuterStrideAtCompileTime),
    Alignment = int(MapOptions) & int(AlignedMask),
    Flags0 = TraitsBase::Flags & (~NestByRefBit),
    Flags = is_lvalue<PlainObjectType>::value ? int(Flags0) : (int(Flags0) & ~LvalueBit)
  };

 private:
  enum { Options };  // Expressions don't have Options
};
}  // namespace internal

/** \class Map
 * \ingroup Core_Module
 *
 * \brief A matrix or vector expression mapping an existing array of data.
 *
 * \tparam PlainObjectType the equivalent matrix type of the mapped data
 * \tparam MapOptions 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, Map assumes the memory layout of an ordinary, contiguous array. This can be overridden by
 * specifying strides. The type passed here must be a specialization of the Stride template, see examples below.
 *
 * This class represents a matrix or vector expression mapping an existing array of data.
 * It can be used to let Eigen interface without any overhead with non-Eigen data structures,
 * such as plain C arrays or structures from other libraries. By default, it assumes that the
 * data is laid out contiguously in memory. You can however override this by explicitly specifying
 * inner and outer strides.
 *
 * Here's an example of simply mapping a contiguous array as a \ref TopicStorageOrders "column-major" matrix:
 * \include Map_simple.cpp
 * Output: \verbinclude Map_simple.out
 *
 * If you need to map non-contiguous arrays, you can do so by specifying strides:
 *
 * Here's an example of mapping an array as a vector, specifying an inner stride, that is, the pointer
 * increment between two consecutive coefficients. Here, we're specifying the inner stride as a compile-time
 * fixed value.
 * \include Map_inner_stride.cpp
 * Output: \verbinclude Map_inner_stride.out
 *
 * Here's an example of mapping an array while specifying an outer stride. Here, since we're mapping
 * as a column-major matrix, 'outer stride' means the pointer increment between two consecutive columns.
 * Here, we're specifying the outer stride as a runtime parameter. Note that here \c OuterStride<> is
 * a short version of \c OuterStride<Dynamic> because the default template parameter of OuterStride
 * is  \c Dynamic
 * \include Map_outer_stride.cpp
 * Output: \verbinclude Map_outer_stride.out
 *
 * For more details and for an example of specifying both an inner and an outer stride, see class Stride.
 *
 * \b Tip: to change the array of data mapped by a Map object, you can use the C++
 * placement new syntax:
 *
 * Example: \include Map_placement_new.cpp
 * Output: \verbinclude Map_placement_new.out
 *
 * This class is the return type of PlainObjectBase::Map() but can also be used directly.
 *
 * \sa PlainObjectBase::Map(), \ref TopicStorageOrders
 */
template <typename PlainObjectType, int MapOptions, typename StrideType>
class Map : public MapBase<Map<PlainObjectType, MapOptions, StrideType> > {
 public:
  typedef MapBase<Map> Base;
  EIGEN_DENSE_PUBLIC_INTERFACE(Map)

  typedef typename Base::PointerType PointerType;
  typedef PointerType PointerArgType;
  EIGEN_DEVICE_FUNC constexpr inline PointerType cast_to_pointer_type(PointerArgType ptr) const { return ptr; }

  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()
           : internal::traits<Map>::OuterStrideAtCompileTime != Dynamic
               ? Index(internal::traits<Map>::OuterStrideAtCompileTime)
           : IsVectorAtCompileTime    ? (this->size() * innerStride())
           : int(Flags) & RowMajorBit ? (this->cols() * innerStride())
                                      : (this->rows() * innerStride());
  }

  /** Constructor in the fixed-size case.
   *
   * \param dataPtr pointer to the array to map
   * \param stride optional Stride object, passing the strides.
   */
  EIGEN_DEVICE_FUNC constexpr explicit inline Map(PointerArgType dataPtr, const StrideType& stride = StrideType())
      : Base(cast_to_pointer_type(dataPtr)), m_stride(stride) {}

  /** Constructor in the dynamic-size vector case.
   *
   * \param dataPtr pointer to the array to map
   * \param size the size of the vector expression
   * \param stride optional Stride object, passing the strides.
   */
  EIGEN_DEVICE_FUNC constexpr inline Map(PointerArgType dataPtr, Index size, const StrideType& stride = StrideType())
      : Base(cast_to_pointer_type(dataPtr), size), m_stride(stride) {}

  /** Constructor in the dynamic-size matrix case.
   *
   * \param dataPtr pointer to the array to map
   * \param rows the number of rows of the matrix expression
   * \param cols the number of columns of the matrix expression
   * \param stride optional Stride object, passing the strides.
   */
  EIGEN_DEVICE_FUNC constexpr inline Map(PointerArgType dataPtr, Index rows, Index cols,
                                         const StrideType& stride = StrideType())
      : Base(cast_to_pointer_type(dataPtr), rows, cols), m_stride(stride) {}

  EIGEN_INHERIT_ASSIGNMENT_OPERATORS(Map)

 protected:
  StrideType m_stride;
};

}  // end namespace Eigen

#endif  // EIGEN_MAP_H