algorithm.hh

// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
#ifndef DUNE_SOLVERS_COMMON_ALGORITHM_HH
#define DUNE_SOLVERS_COMMON_ALGORITHM_HH


#include <dune/common/typeutilities.hh>

#include <dune/istl/multitypeblockvector.hh>

namespace Dune {
namespace Solvers {


// Everything in the next namespace block is just used to implement integralRangeFor
namespace Imp {

template<class ST, ST begin, ST end>
struct StaticForLoop
{
  template<class F, class...Args>
  static void apply(F&& f, Args&&... args)
  {
    f(std::integral_constant<ST, begin>(), std::forward<Args>(args)...);
    StaticForLoop<ST, begin+1, end>::apply(std::forward<F>(f), std::forward<Args>(args)...);
  }
};

template<class ST, ST end>
struct StaticForLoop<ST, end, end>
{
  template<class F, class...Args>
  static void apply(F&& f, Args&&...)
  {}
};

// Check if T is an integral constant
template<class T>
struct IsIntegralConstantHelper
{
    static const bool value = false;
};

template<class T, T t>
struct IsIntegralConstantHelper<std::integral_constant<T, t>>
{
    static const bool value = true;
};

// Check if T is an integral constant
template<class T>
struct IsIntegralConstant : public IsIntegralConstantHelper<std::decay_t<T>>
{};



// Compute t1==t2 either statically or dynamically
template<class T1, class T2>
constexpr auto hybridEqual(const T1& t1, const T2& t2, PriorityTag<1>) -> decltype(T1::value, T2::value, std::integral_constant<bool,T1::value == T2::value>())
{ return {}; }

template<class T1, class T2>
constexpr auto hybridEqual(const T1& t1, const T2& t2, PriorityTag<0>)
{
  return t1==t2;
}

template<class IfFunc, class ElseFunc>
void staticIf(IfFunc&& ifFunc, ElseFunc&& elseFunc, std::false_type)
{
  elseFunc([](auto&& x) { return std::forward<decltype(x)>(x);});
}

template<class IfFunc, class ElseFunc>
void staticIf(IfFunc&& ifFunc, ElseFunc&& elseFunc, std::true_type)
{
  ifFunc([](auto&& x) { return std::forward<decltype(x)>(x);});
}

} //end namespace Imp



/**
 * \brief Hybrid for loop over integral range
 *
 * \tparam Index Raw type of used indices
 * \tparam Begin Type of begin index
 * \tparam End Type of end index
 * \tparam F Type of functor containing the loop body
 * \tparam Args Types of further arguments to the loop body
 *
 * \param begin Initial index
 * \param end One past last index
 * \param f Functor to call in each loop instance
 * \param args Additional arguments to be passed to the functor
 *
 * This is a hybrid for loop that can work on statically and dynamically
 * sized containers. The functor is called with index as first argument
 * and all additional arguments. 
 *
 * This is the static-size overload which is selected if begin and
 * end are both static indices, i.e., integral constants. The loop
 * body is called with std::integral_constant<Index,i> where i
 * is the static index.
 */
template<class Index, class Begin, class End, class F, class... Args,
    std::enable_if_t<Imp::IsIntegralConstant<Begin>::value and Imp::IsIntegralConstant<End>::value, int> = 0>
void integralRangeFor(Begin&& begin, End&& end, F&& f, Args&&... args)
{
  static const Index begin_t = begin;
  static const Index end_t = end;
  Imp::StaticForLoop<Index, begin_t, end_t>::apply(std::forward<F>(f), std::forward<Args>(args)...);
}

/**
 * \brief Hybrid for loop over integral range
 *
 * \tparam Index Raw type of used indices
 * \tparam Begin Type of begin index
 * \tparam End Type of end index
 * \tparam F Type of functor containing the loop body
 * \tparam Args Types of further arguments to the loop body
 *
 * \param begin Initial index
 * \param end One past last index
 * \param f Functor to call in each loop instance
 * \param args Additional arguments to be passed to the functor
 *
 * This is a hybrid for loop that can work on statically and dynamically
 * sized containers. The functor is called with index as first argument
 * and all additional arguments. 
 *
 * This is the dynamic-size overload which is selected if either begin or
 * end is a dynamic index, i.e., not an integral constant. The loop
 * body is called with indices of type Index.
 */
template<class Index, class Begin, class End, class F, class... Args,
    std::enable_if_t<not(Imp::IsIntegralConstant<Begin>::value and Imp::IsIntegralConstant<End>::value), int> = 0>
void integralRangeFor(Begin&& begin, End&& end, F&& f, Args&&... args)
{
  for(Index i=begin; i != end; ++i)
    f(i, std::forward<Args>(args)...);
}



// Everything in the next namespace block is just used to implement StaticSize, HasStaticSize, hybridSize
namespace Imp {

// As a last resort try if there's a static constexpr size()
template<class T>
constexpr auto staticSize(const T*, const PriorityTag<0>&)
  -> decltype(std::integral_constant<std::size_t,T::size()>())
{
  return {};
}

// Try if class has constexpr default constructor and size method
template<class T>
constexpr auto staticSize(const T*, const PriorityTag<1>&)
  -> decltype(std::integral_constant<std::size_t,T().size()>())
{
  return {};
}

// Try if tuple_size is implemented for class
template<class T>
constexpr auto staticSize(const T*, const PriorityTag<2>&)
  -> decltype(std::integral_constant<std::size_t,std::tuple_size<T>::value>())
{
  return {};
}

// Try if tuple_size is implemented for class
template<class T, int i>
constexpr auto staticSize(const Dune::FieldVector<T, i>*, const PriorityTag<3>&)
  -> decltype(std::integral_constant<std::size_t,i>())
{
  return {};
}

template<class T>
constexpr std::false_type hasStaticSize(const T* t, const PriorityTag<0>& p)
{
  return {};
}

template<class T>
constexpr auto hasStaticSize(const T* t, const PriorityTag<1>& p)
  -> decltype(staticSize(t ,PriorityTag<42>()), std::true_type())
{
  return {};
}

}



/**
 * \brief Check if type is a statically sized container
 *
 * \ingroup Utility
 *
 * Derives from std::true_type or std::false_type
 */
template<class T>
struct HasStaticSize :
  public decltype(Imp::hasStaticSize((typename std::decay<T>::type*)(nullptr), PriorityTag<42>()))
{};



/**
 * \brief Obtain size of statically sized container
 *
 * \ingroup Utility
 *
 * Derives from std::integral_constant<std::size_t, size>
 */
template<class T>
struct StaticSize :
  public decltype(Imp::staticSize((typename std::decay<T>::type*)(nullptr), PriorityTag<42>()))
{};



/**
 * \brief Hybrid size query
 *
 * \tparam T Type of container whose size is queried
 *
 * \param t Container whose size is queried
 *
 * This function is hybrid in the sense that it returns a statically
 * encoded size, i.e., an integral_constant if possible and the
 * dynamic result of the t.size() method otherwise.
 *
 * This is the static-size overload which returns the size i
 * as std::integral_constant<std::size_t, i>.
 */
template<class T,
    std::enable_if_t<HasStaticSize<T>::value, int> = 0>
constexpr auto hybridSize(const T& t)
{
  return Imp::staticSize((T*)(nullptr), PriorityTag<42>());
}

/**
 * \brief Hybrid size query
 *
 * \tparam T Type of container whose size is queried
 *
 * \param t Container whose size is queried
 *
 * This function is hybrid in the sense that it returns a statically
 * encoded size, i.e., an integral_constant if possible and the
 * dynamic result of the *.size() method otherwise.
 *
 * This is the dynamic-size overload which returns the result
 * of t.size().
 */
template<class T,
    std::enable_if_t<not HasStaticSize<T>::value, int> = 0>
constexpr auto hybridSize(const T& t)
{
  return t.size();
}



/**
 * \brief Hybrid for loop over sparse range
 */
template<class... T, class F>
void sparseRangeFor(const Dune::MultiTypeBlockVector<T...>& range, F&& f)
{
  integralRangeFor<std::size_t>(Indices::_0, hybridSize(range), [&](auto&& i) {
      f(range[i], i);
  });
}



/**
 * \brief Hybrid for loop over sparse range
 */
template<class Range, class F>
void sparseRangeFor(Range&& range, F&& f)
{
  auto it = range.begin();
  auto end = range.end();
  for(; it!=end; ++it)
    f(*it, it.index());
}



/**
 * \brief Hybrid equality comparison
 *
 * If both types have a static member value, the result of comparing
 * these is returned as std::integral_constant<bool, *>. Otherwise
 * the result of a runtime comparison of t1 and t2 is directly returned.
 */
template<class T1, class T2>
constexpr auto hybridEqual(const T1& t1, const T2& t2)
{
  return Imp::hybridEqual(t1, t2, PriorityTag<1>());
}


/**
 * \brief Static if emulation
 *
 * This will call either ifFunc or elseFunc depending
 * on the condition. In any case a single argument
 * will be passed to the called function. This will always
 * be the indentity function. Passing an expression through
 * this function will lead to lazy evaluation. This way both
 * 'branches' can contain expressions that are only valid
 * within this branch.
 */
template<bool condition, class IfFunc, class ElseFunc>
void staticIf(IfFunc&& ifFunc, ElseFunc&& elseFunc)
{
  Imp::staticIf(std::forward<IfFunc>(ifFunc), std::forward<ElseFunc>(elseFunc), std::integral_constant<bool, condition>());
}



namespace Imp {

template<bool condition, class IfFunc, class ElseFunc>
void hybridIf(const std::integral_constant<bool, condition>&, IfFunc&& ifFunc, ElseFunc&& elseFunc)
{
  staticIf<condition>(std::forward<IfFunc>(ifFunc), std::forward<ElseFunc>(elseFunc));
}

template<class IfFunc, class ElseFunc>
void hybridIf(const bool& condition, IfFunc&& ifFunc, ElseFunc&& elseFunc)
{
  if (condition)
    ifFunc([](auto&& x) { return std::forward<decltype(x)>(x);});
  else
    elseFunc([](auto&& x) { return std::forward<decltype(x)>(x);});
}

} // namespace Imp



/**
 * \brief Hybrid if
 *
 * This will call either ifFunc or elseFunc depending
 * on the condition. In any case a single argument
 * will be passed to the called function. This will always
 * be the indentity function. Passing an expression through
 * this function will lead to lazy evaluation. This way both
 * 'branches' can contain expressions that are only valid
 * within this branch if the condition is a std::integral_constant<bool,*>.
 */
template<class Condition, class IfFunc, class ElseFunc>
void hybridIf(const Condition& condition, IfFunc&& ifFunc, ElseFunc&& elseFunc)
{
  Imp::hybridIf(condition, std::forward<IfFunc>(ifFunc), std::forward<ElseFunc>(elseFunc));
}



/**
 * \brief Hybrid if
 *
 * This provides a hybridIf with empty else clause.
 */
template<class Condition, class IfFunc>
void hybridIf(const Condition& condition, IfFunc&& ifFunc)
{
  hybridIf(condition, std::forward<IfFunc>(ifFunc), [](auto&& i) {});
}

} // namespace Solvers
} // namespace Dune


#endif// DUNE_SOLVERS_COMMON_FORLOOP_HH