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 // Copyright (C) 2007 Trustees of Indiana University
 
 // Authors: Douglas Gregor
 //          Andrew Lumsdaine
 
 // Use, modification and distribution is subject to the Boost Software
 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt)
 
 /** @file group.hpp
  *
  *  This header defines the @c group class, which allows one to
  *  manipulate and query groups of processes.
  */
 #ifndef BOOST_MPI_GROUP_HPP
 #define BOOST_MPI_GROUP_HPP
 
 #include <boost/mpi/exception.hpp>
 #include <boost/mpi/detail/antiques.hpp>
 #include <boost/shared_ptr.hpp>
 #include <boost/optional.hpp>
 #include <vector>
 
 namespace boost { namespace mpi {
 
 /**
  * @brief A @c group is a representation of a subset of the processes
  * within a @c communicator.
  *
  * The @c group class allows one to create arbitrary subsets of the
  * processes within a communicator. One can compute the union,
  * intersection, or difference of two groups, or create new groups by
  * specifically including or excluding certain processes. Given a
  * group, one can create a new communicator containing only the
  * processes in that group.
  */
 class BOOST_MPI_DECL group
 {
 public:
   /**
    * @brief Constructs an empty group.
    */
   group() : group_ptr() { }
 
   /**
    * @brief Constructs a group from an @c MPI_Group.
    *
    * This routine allows one to construct a Boost.MPI @c group from a
    * C @c MPI_Group. The @c group object can (optionally) adopt the @c
    * MPI_Group, after which point the @c group object becomes
    * responsible for freeing the @c MPI_Group when the last copy of @c
    * group disappears.
    *
    * @param in_group The @c MPI_Group used to construct this @c group.
    *
    * @param adopt Whether the @c group should adopt the @c
    * MPI_Group. When true, the @c group object (or one of its copies)
    * will free the group (via @c MPI_Comm_free) when the last copy is
    * destroyed. Otherwise, the user is responsible for calling @c
    * MPI_Group_free.
    */
   group(const MPI_Group& in_group, bool adopt);
 
   /**
    * @brief Determine the rank of the calling process in the group.
    * 
    * This routine is equivalent to @c MPI_Group_rank.
    *
    * @returns The rank of the calling process in the group, which will
    * be a value in [0, size()). If the calling process is not in the
    * group, returns an empty value.
    */
   optional<int> rank() const;
 
   /**
    * @brief Determine the number of processes in the group.
    *
    * This routine is equivalent to @c MPI_Group_size.
    *
    * @returns The number of processes in the group.
    */
   int size() const;
 
   /**
    * @brief Translates the ranks from one group into the ranks of the
    * same processes in another group.
    *
    * This routine translates each of the integer rank values in the
    * iterator range @c [first, last) from the current group into rank
    * values of the corresponding processes in @p to_group. The
    * corresponding rank values are written via the output iterator @c
    * out. When there is no correspondence between a rank in the
    * current group and a rank in @c to_group, the value @c
    * MPI_UNDEFINED is written to the output iterator.
    *
    * @param first Beginning of the iterator range of ranks in the
    * current group.
    *
    * @param last Past the end of the iterator range of ranks in the
    * current group.
    *
    * @param to_group The group that we are translating ranks to.
    *
    * @param out The output iterator to which the translated ranks will
    * be written.
    *
    * @returns the output iterator, which points one step past the last
    * rank written.
    */
   template<typename InputIterator, typename OutputIterator>
   OutputIterator translate_ranks(InputIterator first, InputIterator last,
                                  const group& to_group, OutputIterator out);
 
   /**
    * @brief Determines whether the group is non-empty.
    *
    * @returns True if the group is not empty, false if it is empty.
    */
   operator bool() const { return (bool)group_ptr; }
 
   /**
    * @brief Retrieves the underlying @c MPI_Group associated with this
    * group.
    *
    * @returns The @c MPI_Group handle manipulated by this object. If
    * this object represents the empty group, returns @c
    * MPI_GROUP_EMPTY.
    */
   operator MPI_Group() const
   {
     if (group_ptr)
       return *group_ptr;
     else
       return MPI_GROUP_EMPTY;
   }
 
   /**
    *  @brief Creates a new group including a subset of the processes
    *  in the current group.
    *
    *  This routine creates a new @c group which includes only those
    *  processes in the current group that are listed in the integer
    *  iterator range @c [first, last). Equivalent to @c
    *  MPI_Group_incl.
    *
    *  @c first The beginning of the iterator range of ranks to include.
    *
    *  @c last Past the end of the iterator range of ranks to include.
    *
    *  @returns A new group containing those processes with ranks @c
    *  [first, last) in the current group.
    */
   template<typename InputIterator>
   group include(InputIterator first, InputIterator last);
 
   /**
    *  @brief Creates a new group from all of the processes in the
    *  current group, exluding a specific subset of the processes.
    *
    *  This routine creates a new @c group which includes all of the
    *  processes in the current group except those whose ranks are
    *  listed in the integer iterator range @c [first,
    *  last). Equivalent to @c MPI_Group_excl.
    *
    *  @c first The beginning of the iterator range of ranks to exclude.
    *
    *  @c last Past the end of the iterator range of ranks to exclude.
    *
    *  @returns A new group containing all of the processes in the
    *  current group except those processes with ranks @c [first, last)
    *  in the current group. 
    */
   template<typename InputIterator>
   group exclude(InputIterator first, InputIterator last);
   
 
 protected:
   /**
    * INTERNAL ONLY
    *
    * Function object that frees an MPI group and deletes the
    * memory associated with it. Intended to be used as a deleter with
    * shared_ptr.
    */
   struct group_free
   {
     void operator()(MPI_Group* comm) const
     {
       int finalized;
       BOOST_MPI_CHECK_RESULT(MPI_Finalized, (&finalized));
       if (!finalized)
         BOOST_MPI_CHECK_RESULT(MPI_Group_free, (comm));
       delete comm;
     }
   };
 
   /**
    * The underlying MPI group. This is a shared pointer, so the actual
    * MPI group which will be shared among all related instances of the
    * @c group class. When there are no more such instances, the group
    * will be automatically freed.
    */
   shared_ptr<MPI_Group> group_ptr;
 };
 
 /**
  * @brief Determines whether two process groups are identical.
  *
  * Equivalent to calling @c MPI_Group_compare and checking whether the
  * result is @c MPI_IDENT.
  *
  * @returns True when the two process groups contain the same
  * processes in the same order.
  */
 BOOST_MPI_DECL bool operator==(const group& g1, const group& g2);
 
 /**
  * @brief Determines whether two process groups are not identical.
  *
  * Equivalent to calling @c MPI_Group_compare and checking whether the
  * result is not @c MPI_IDENT.
  *
  * @returns False when the two process groups contain the same
  * processes in the same order.
  */
 inline bool operator!=(const group& g1, const group& g2)
 { 
   return !(g1 == g2);
 }
 
 /**
  * @brief Computes the union of two process groups.
  *
  * This routine returns a new @c group that contains all processes
  * that are either in group @c g1 or in group @c g2 (or both). The
  * processes that are in @c g1 will be first in the resulting group,
  * followed by the processes from @c g2 (but not also in @c
  * g1). Equivalent to @c MPI_Group_union.
  */
 BOOST_MPI_DECL group operator|(const group& g1, const group& g2);
 
 /**
  * @brief Computes the intersection of two process groups.
  *
  * This routine returns a new @c group that contains all processes
  * that are in group @c g1 and in group @c g2, ordered in the same way
  * as @c g1. Equivalent to @c MPI_Group_intersection.
  */
 BOOST_MPI_DECL group operator&(const group& g1, const group& g2);
 
 /**
  * @brief Computes the difference between two process groups.
  *
  * This routine returns a new @c group that contains all processes
  * that are in group @c g1 but not in group @c g2, ordered in the same way
  * as @c g1. Equivalent to @c MPI_Group_difference.
  */
 BOOST_MPI_DECL group operator-(const group& g1, const group& g2);
 
 /************************************************************************
  * Implementation details                                               *
  ************************************************************************/
 template<typename InputIterator, typename OutputIterator>
 OutputIterator 
 group::translate_ranks(InputIterator first, InputIterator last,
                        const group& to_group, OutputIterator out)
 {
   std::vector<int> in_array(first, last);
   if (in_array.empty())
     return out;
 
   std::vector<int> out_array(in_array.size());
   BOOST_MPI_CHECK_RESULT(MPI_Group_translate_ranks,
                          ((MPI_Group)*this,
                           in_array.size(),
                           detail::c_data(in_array),
                           (MPI_Group)to_group,
                           detail::c_data(out_array)));
 
   for (std::vector<int>::size_type i = 0, n = out_array.size(); i < n; ++i)
     *out++ = out_array[i];
   return out;
 }
 
 /**
  * INTERNAL ONLY
  * 
  * Specialization of translate_ranks that handles the one case where
  * we can avoid any memory allocation or copying.
  */
 template<> 
 BOOST_MPI_DECL int*
 group::translate_ranks(int* first, int* last, const group& to_group, int* out);
 
 template<typename InputIterator>
 group group::include(InputIterator first, InputIterator last)
 {
   if (first == last)
     return group();
 
   std::vector<int> ranks(first, last);
   MPI_Group result;
   BOOST_MPI_CHECK_RESULT(MPI_Group_incl,
                          ((MPI_Group)*this, ranks.size(), detail::c_data(ranks), &result));
   return group(result, /*adopt=*/true);
 }
 
 /**
  * INTERNAL ONLY
  * 
  * Specialization of group::include that handles the one case where we
  * can avoid any memory allocation or copying before creating the
  * group.
  */
 template<> BOOST_MPI_DECL group group::include(int* first, int* last);
 
 template<typename InputIterator>
 group group::exclude(InputIterator first, InputIterator last)
 {
   if (first == last)
     return group();
 
   std::vector<int> ranks(first, last);
   MPI_Group result;
   BOOST_MPI_CHECK_RESULT(MPI_Group_excl,
                          ((MPI_Group)*this, ranks.size(), detail::c_data(ranks), &result));
   return group(result, /*adopt=*/true);
 }
 
 /**
  * INTERNAL ONLY
  * 
  * Specialization of group::exclude that handles the one case where we
  * can avoid any memory allocation or copying before creating the
  * group.
  */
 template<> BOOST_MPI_DECL group group::exclude(int* first, int* last);
 
 } } // end namespace boost::mpi
 
 #endif // BOOST_MPI_GROUP_HPP

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