[boost] Unrolling loops

From: Guy Peleg (guy.peleg_at_[hidden])
Date: 2006-11-09 09:56:55

Hi,


Is there any interest in a library which unrolls loops when traversing N
times through containers? (where N is known in compile time)


For example, 'fixed_size_for_each':


// IT - Iterator

// N -  The number of elements

template <typename IT, int N>

struct fixed_size_for_each_impl;



// ================

// Specialization 1:

template <typename IT, int N>

struct fixed_size_for_each_impl

{

  template <class F>

  void operator()(IT  it,

                  F&  op)

  {

      op(*it);


      fixed_size_for_each_impl<IT, N-1> tail;


      tail(++it, op);

  }

};


// ================

// Specialization 2 ('stop condition'):

template <typename IT>

struct fixed_size_for_each_impl<IT, 1>

{

  template <class F>

  void operator()(IT  it,

                  F&  op)

  {

      op(*it);

  }

};


// ================

// A sort of 'for_each' algorithm

// that traverses N times through some

// container while unrolling the loop

template<int N, typename IT, typename F>

F fixed_size_for_each(IT it,

                      F  op)

{

  fixed_size_for_each_impl<IT, N>()(it, op);

  return op;

}


// ================

// Overloaded method especially for boost::array

// because we know the number of elements (static_size)

template<typename F, typename T, int N>

F fixed_size_for_each(boost::array<T, N>& a,

                      F                   op)

{

  typedef boost::array<T, N> boost_array;

  return fixed_size_for_each<boost_array::static_size>(a.begin(), op);

}


Possible use:

boost::array<Shape *, 4> a;

....

fixed_size_for_each(a, mem_fun(&Shape::draw));



Other algorithms (e.g. find) can be done too, if there is a need I'll be
happy to submit a suggestion.


Thanks,


Guy


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