Eigen/src/Core/Stride.h

// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2010 Benoit Jacob <jacob.benoit.1@gmail.com>
//
// 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/.
// SPDX-License-Identifier: MPL-2.0

#ifndef EIGEN_STRIDE_H
#define EIGEN_STRIDE_H

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

namespace Eigen {

/** \class Stride
 * \ingroup Core_Module
 *
 * \brief Holds strides information for Map
 *
 * This class holds the strides information for mapping arrays with strides with class Map.
 *
 * It holds two values: the inner stride and the outer stride.
 *
 * The inner stride is the pointer increment between two consecutive entries within a given row of a
 * row-major matrix or within a given column of a column-major matrix.
 *
 * The outer stride is the pointer increment between two consecutive rows of a row-major matrix or
 * between two consecutive columns of a column-major matrix.
 *
 * These two values can be passed either at compile-time as template parameters, or at runtime as
 * arguments to the constructor.
 *
 * Indeed, this class takes two template parameters:
 *  \tparam OuterStrideAtCompileTime_ the outer stride, or Dynamic if you want to specify it at runtime.
 *  \tparam InnerStrideAtCompileTime_ the inner stride, or Dynamic if you want to specify it at runtime.
 *
 * Here is an example:
 * \include Map_general_stride.cpp
 * Output: \verbinclude Map_general_stride.out
 *
 * Both strides can be negative. However, a negative stride of -1 cannot be specified at compile time
 * because of the ambiguity with Dynamic which is defined to -1 (historically, negative strides were
 * not allowed).
 *
 * Note that for compile-time vectors (ColsAtCompileTime==1 or RowsAtCompileTime==1),
 * the inner stride is the pointer increment between two consecutive elements,
 * regardless of storage layout.
 *
 * \sa class InnerStride, class OuterStride, \ref TopicStorageOrders
 */
template <int OuterStrideAtCompileTime_, int InnerStrideAtCompileTime_>
class Stride {
 public:
  using Index = Eigen::Index;  ///< \deprecated since Eigen 3.3
  enum { InnerStrideAtCompileTime = InnerStrideAtCompileTime_, OuterStrideAtCompileTime = OuterStrideAtCompileTime_ };

  /** Default constructor, for use when strides are fixed at compile time */
  EIGEN_DEVICE_FUNC constexpr Stride() : m_outer(OuterStrideAtCompileTime), m_inner(InnerStrideAtCompileTime) {
    eigen_assert(InnerStrideAtCompileTime != Dynamic && OuterStrideAtCompileTime != Dynamic);
  }

  /** Constructor allowing to pass the strides at runtime */
  EIGEN_DEVICE_FUNC constexpr Stride(Index outerStride, Index innerStride)
      : m_outer(outerStride), m_inner(innerStride) {}

  /** Copy constructor */
  EIGEN_DEVICE_FUNC constexpr Stride(const Stride& other) = default;

  /** Copy assignment operator */
  EIGEN_DEVICE_FUNC constexpr Stride& operator=(const Stride& other) {
    m_outer.setValue(other.outer());
    m_inner.setValue(other.inner());
    return *this;
  }

  /** \returns the outer stride */
  EIGEN_DEVICE_FUNC constexpr Index outer() const { return m_outer.value(); }
  /** \returns the inner stride */
  EIGEN_DEVICE_FUNC constexpr Index inner() const { return m_inner.value(); }

 protected:
  internal::variable_if_dynamic<Index, OuterStrideAtCompileTime> m_outer;
  internal::variable_if_dynamic<Index, InnerStrideAtCompileTime> m_inner;
};

/** \brief Convenience specialization of Stride to specify only an inner stride
 * See class Map for some examples */
template <int Value>
class InnerStride : public Stride<0, Value> {
  using Base = Stride<0, Value>;

 public:
  EIGEN_DEVICE_FUNC constexpr InnerStride() = default;
  EIGEN_DEVICE_FUNC constexpr InnerStride(Index v) : Base(0, v) {}  // FIXME making this explicit could break valid code
};

/** \brief Convenience specialization of Stride to specify only an outer stride
 * See class Map for some examples */
template <int Value>
class OuterStride : public Stride<Value, 0> {
  using Base = Stride<Value, 0>;

 public:
  EIGEN_DEVICE_FUNC constexpr OuterStride() = default;
  EIGEN_DEVICE_FUNC constexpr OuterStride(Index v) : Base(v, 0) {}  // FIXME making this explicit could break valid code
};

}  // end namespace Eigen

#endif  // EIGEN_STRIDE_H