gcc/libstdc++-v3/include/parallel/unique_copy.h

// -*- C++ -*-

// Copyright (C) 2007 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
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// of the GNU General Public License as published by the Free Software
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// version.

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// General Public License for more details.

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/** @file parallel/unique_copy.h
 *  @brief Parallel implementations of std::unique_copy().
 *  This file is a GNU parallel extension to the Standard C++ Library.
 */

// Written by Robert Geisberger and Robin Dapp.

#ifndef _GLIBCXX_PARALLEL_UNIQUE_H
#define _GLIBCXX_PARALLEL_UNIQUE_H 1

#include <parallel/parallel.h>
#include <parallel/multiseq_selection.h>

namespace __gnu_parallel
{

  /** @brief Parallel std::unique_copy(), without explicit equality predicate.
   *  @param first Begin iterator of input sequence.
   *  @param last End iterator of input sequence.
   *  @param result Begin iterator of result sequence.
   *  @param binary_pred Equality predicate.
   *  @return End iterator of result sequence. */
  template<typename InputIterator, class OutputIterator, class BinaryPredicate>
  inline OutputIterator
  parallel_unique_copy(InputIterator first, InputIterator last,
		       OutputIterator result, BinaryPredicate binary_pred)
  {
    _GLIBCXX_CALL(last - first)

    typedef std::iterator_traits<InputIterator> traits_type;
    typedef typename traits_type::value_type value_type;
    typedef typename traits_type::difference_type difference_type;

    difference_type size = last - first;
    int num_threads = __gnu_parallel::get_max_threads();
    difference_type counter[num_threads + 1];

    if (size == 0)
      return result;

    // Let the first thread process two parts.
    difference_type borders[num_threads + 2];
    __gnu_parallel::equally_split(size, num_threads + 1, borders);

    // First part contains at least one element.
#pragma omp parallel num_threads(num_threads)
    {
      int iam = omp_get_thread_num();

      difference_type begin, end;

      // Check for length without duplicates
      // Needed for position in output
      difference_type i = 0;
      OutputIterator out = result;
      if (iam == 0)
	{
	  begin = borders[0] + 1;	// == 1
	  end = borders[iam + 1];

	  i++;
	  new (static_cast<void *>(&*out)) value_type(*first);
	  out++;

	  for (InputIterator iter = first + begin; iter < first + end; ++iter)
	    {
	      if (!binary_pred(*iter, *(iter-1)))
		{
		  i++;
		  new (static_cast<void *>(&*out)) value_type(*iter);
		  out++;
		}
	    }
	}
      else
	{
	  begin = borders[iam]; //one part
	  end = borders[iam + 1];

	  for (InputIterator iter = first + begin; iter < first + end; ++iter)
	    {
	      if (!binary_pred(*iter, *(iter-1)))
		{
		  i++;
		}
	    }
	}
      counter[iam] = i;

      // Last part still untouched.
      difference_type begin_output;

#pragma omp barrier

      // Store result in output on calculated positions.
      begin_output = 0;

      if (iam == 0)
	{
	  for (int t = 0; t < num_threads; t++)
	    begin_output += counter[t];

	  i = 0;

	  OutputIterator iter_out = result + begin_output;

	  begin = borders[num_threads];
	  end = size;

	  for (InputIterator iter = first + begin; iter < first + end; ++iter)
	    {
	      if (iter == first || !binary_pred(*iter, *(iter-1)))
		{
		  i++;
		  new (static_cast<void *>(&*iter_out)) value_type(*iter);
		  iter_out++;
		}
	    }

	  counter[num_threads] = i;
	}
      else
	{
	  for (int t = 0; t < iam; t++)
	    begin_output += counter[t];

	  OutputIterator iter_out = result + begin_output;
	  for (InputIterator iter = first + begin; iter < first + end; ++iter)
	    {
	      if (!binary_pred(*iter, *(iter-1)))
		{
		  new (static_cast<void *> (&*iter_out)) value_type(*iter);
		  iter_out++;
		}
	    }
	}
    }

    difference_type end_output = 0;
    for (int t = 0; t < num_threads + 1; t++)
      end_output += counter[t];

    return result + end_output;
  }

  /** @brief Parallel std::unique_copy(), without explicit equality predicate
   *  @param first Begin iterator of input sequence.
   *  @param last End iterator of input sequence.
   *  @param result Begin iterator of result sequence.
   *  @return End iterator of result sequence. */
  template<typename InputIterator, class OutputIterator>
  inline OutputIterator
  parallel_unique_copy(InputIterator first, InputIterator last,
		       OutputIterator result)
  {
    typedef typename std::iterator_traits<InputIterator>::value_type value_type;

    return parallel_unique_copy(first, last, result, std::equal_to<value_type>());
  }

}//namespace __gnu_parallel

#endif