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      1 // This file is part of Eigen, a lightweight C++ template library
      2 // for linear algebra.
      3 //
      4 // Copyright (C) 2010 Benoit Jacob <jacob.benoit.1 (at) gmail.com>
      5 //
      6 // This Source Code Form is subject to the terms of the Mozilla
      7 // Public License v. 2.0. If a copy of the MPL was not distributed
      8 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
      9 
     10 #ifndef EIGEN_STRIDE_H
     11 #define EIGEN_STRIDE_H
     12 
     13 namespace Eigen {
     14 
     15 /** \class Stride
     16   * \ingroup Core_Module
     17   *
     18   * \brief Holds strides information for Map
     19   *
     20   * This class holds the strides information for mapping arrays with strides with class Map.
     21   *
     22   * It holds two values: the inner stride and the outer stride.
     23   *
     24   * The inner stride is the pointer increment between two consecutive entries within a given row of a
     25   * row-major matrix or within a given column of a column-major matrix.
     26   *
     27   * The outer stride is the pointer increment between two consecutive rows of a row-major matrix or
     28   * between two consecutive columns of a column-major matrix.
     29   *
     30   * These two values can be passed either at compile-time as template parameters, or at runtime as
     31   * arguments to the constructor.
     32   *
     33   * Indeed, this class takes two template parameters:
     34   *  \param _OuterStrideAtCompileTime the outer stride, or Dynamic if you want to specify it at runtime.
     35   *  \param _InnerStrideAtCompileTime the inner stride, or Dynamic if you want to specify it at runtime.
     36   *
     37   * Here is an example:
     38   * \include Map_general_stride.cpp
     39   * Output: \verbinclude Map_general_stride.out
     40   *
     41   * \sa class InnerStride, class OuterStride, \ref TopicStorageOrders
     42   */
     43 template<int _OuterStrideAtCompileTime, int _InnerStrideAtCompileTime>
     44 class Stride
     45 {
     46   public:
     47     typedef DenseIndex Index;
     48     enum {
     49       InnerStrideAtCompileTime = _InnerStrideAtCompileTime,
     50       OuterStrideAtCompileTime = _OuterStrideAtCompileTime
     51     };
     52 
     53     /** Default constructor, for use when strides are fixed at compile time */
     54     Stride()
     55       : m_outer(OuterStrideAtCompileTime), m_inner(InnerStrideAtCompileTime)
     56     {
     57       eigen_assert(InnerStrideAtCompileTime != Dynamic && OuterStrideAtCompileTime != Dynamic);
     58     }
     59 
     60     /** Constructor allowing to pass the strides at runtime */
     61     Stride(Index outerStride, Index innerStride)
     62       : m_outer(outerStride), m_inner(innerStride)
     63     {
     64       eigen_assert(innerStride>=0 && outerStride>=0);
     65     }
     66 
     67     /** Copy constructor */
     68     Stride(const Stride& other)
     69       : m_outer(other.outer()), m_inner(other.inner())
     70     {}
     71 
     72     /** \returns the outer stride */
     73     inline Index outer() const { return m_outer.value(); }
     74     /** \returns the inner stride */
     75     inline Index inner() const { return m_inner.value(); }
     76 
     77   protected:
     78     internal::variable_if_dynamic<Index, OuterStrideAtCompileTime> m_outer;
     79     internal::variable_if_dynamic<Index, InnerStrideAtCompileTime> m_inner;
     80 };
     81 
     82 /** \brief Convenience specialization of Stride to specify only an inner stride
     83   * See class Map for some examples */
     84 template<int Value = Dynamic>
     85 class InnerStride : public Stride<0, Value>
     86 {
     87     typedef Stride<0, Value> Base;
     88   public:
     89     typedef DenseIndex Index;
     90     InnerStride() : Base() {}
     91     InnerStride(Index v) : Base(0, v) {}
     92 };
     93 
     94 /** \brief Convenience specialization of Stride to specify only an outer stride
     95   * See class Map for some examples */
     96 template<int Value = Dynamic>
     97 class OuterStride : public Stride<Value, 0>
     98 {
     99     typedef Stride<Value, 0> Base;
    100   public:
    101     typedef DenseIndex Index;
    102     OuterStride() : Base() {}
    103     OuterStride(Index v) : Base(v,0) {}
    104 };
    105 
    106 } // end namespace Eigen
    107 
    108 #endif // EIGEN_STRIDE_H
    109