path: root/libstdc++-v3/include/parallel/find.h

/// -*- C++ -*-

// Copyright (C) 2007 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the terms
// of the GNU General Public License as published by the Free Software
// Foundation; either version 2, or (at your option) any later
// version.

// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this library; see the file COPYING.  If not, write to
// the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
// MA 02111-1307, USA.

// As a special exception, you may use this file as part of a free
// software library without restriction.  Specifically, if other files
// instantiate templates or use macros or inline functions from this
// file, or you compile this file and link it with other files to
// produce an executable, this file does not by itself cause the
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/** @file parallel/find.h
 *  @brief Parallel implementation base for std::find(), std::equal()
 *  and related functions.
 *  This file is a GNU parallel extension to the Standard C++ Library.
 */

// Written by Felix Putze and Johannes Singler.

#ifndef _GLIBCXX_PARALLEL_FIND_H
#define _GLIBCXX_PARALLEL_FIND_H 1

#include <bits/stl_algobase.h>

#include <parallel/features.h>
#include <parallel/parallel.h>
#include <parallel/compatibility.h>
#include <parallel/equally_split.h>

namespace __gnu_parallel
{
  /** 
   *  @brief Parallel std::find, switch for different algorithms.
   *  @param begin1 Begin iterator of first sequence.
   *  @param end1 End iterator of first sequence.
   *  @param begin2 Begin iterator of second sequence. Must have same
   *  length as first sequence.
   *  @param pred Find predicate.
   *  @param selector Functionality (e. g. std::find_if (), std::equal(),...)
   *  @return Place of finding in both sequences. 
   */
  template<typename RandomAccessIterator1, typename RandomAccessIterator2, typename Pred, typename Selector>
  std::pair<RandomAccessIterator1, RandomAccessIterator2>
  find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
		RandomAccessIterator2 begin2, Pred pred, Selector selector)
  {
    switch (Settings::find_distribution)
      {
      case Settings::GROWING_BLOCKS:
	return find_template(begin1, end1, begin2, pred, selector, growing_blocks_tag());
      case Settings::CONSTANT_SIZE_BLOCKS:
	return find_template(begin1, end1, begin2, pred, selector, constant_size_blocks_tag());
      case Settings::EQUAL_SPLIT:
	return find_template(begin1, end1, begin2, pred, selector, equal_split_tag());
      default:
	_GLIBCXX_PARALLEL_ASSERT(false);
	return std::make_pair(begin1, begin2);
      }
  }

#if _GLIBCXX_FIND_EQUAL_SPLIT

  /** 
   *  @brief Parallel std::find, equal splitting variant.
   *  @param begin1 Begin iterator of first sequence.
   *  @param end1 End iterator of first sequence.
   *  @param begin2 Begin iterator of second sequence. Second sequence
   *  must have same length as first sequence.
   *  @param pred Find predicate.
   *  @param selector Functionality (e. g. std::find_if (), std::equal(),...)
   *  @return Place of finding in both sequences. 
   */
  template<typename RandomAccessIterator1, typename RandomAccessIterator2, typename Pred, typename Selector>
  std::pair<RandomAccessIterator1, RandomAccessIterator2>
  find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1, RandomAccessIterator2 begin2, Pred pred, Selector selector, equal_split_tag)
  {
    _GLIBCXX_CALL(end1 - begin1)

    typedef std::iterator_traits<RandomAccessIterator1> traits_type;
    typedef typename traits_type::difference_type difference_type;
    typedef typename traits_type::value_type value_type;

    difference_type length = end1 - begin1;

    difference_type result = length;

    const thread_index_t num_threads = get_max_threads();

    // XXX VLA error.
    difference_type borders[num_threads + 1];
    equally_split(length, num_threads, borders);

#pragma omp parallel shared(result) num_threads(num_threads)
    {
      int iam = omp_get_thread_num();
      difference_type pos = borders[iam], limit = borders[iam + 1];

      RandomAccessIterator1 i1 = begin1 + pos;
      RandomAccessIterator2 i2 = begin2 + pos;
      for (; pos < limit; pos++)
	{
#pragma omp flush(result)
	  // Result has been set to something lower.
	  if (result < pos)
	    break;

	  if (selector(i1, i2, pred))
	    {
#pragma omp critical (result)
	      if (result > pos)
		result = pos;
	      break;
	    }
	  i1++;
	  i2++;
	}
    }
    return std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result, begin2 + result);
  }

#endif

#if _GLIBCXX_FIND_GROWING_BLOCKS

  /** 
   *  @brief Parallel std::find, growing block size variant.
   *  @param begin1 Begin iterator of first sequence.
   *  @param end1 End iterator of first sequence.
   *  @param begin2 Begin iterator of second sequence. Second sequence
   *  must have same length as first sequence.
   *  @param pred Find predicate.
   *  @param selector Functionality (e. g. std::find_if (), std::equal(),...)
   *  @return Place of finding in both sequences.
   *  @see __gnu_parallel::Settings::find_sequential_search_size
   *  @see __gnu_parallel::Settings::find_initial_block_size
   *  @see __gnu_parallel::Settings::find_maximum_block_size
   *  @see __gnu_parallel::Settings::find_increasing_factor
   *
   *  There are two main differences between the growing blocks and
   *  the constant-size blocks variants.
   *  1. For GB, the block size grows; for CSB, the block size is fixed.

   *  2. For GB, the blocks are allocated dynamically;
   *     for CSB, the blocks are allocated in a predetermined manner,
   *     namely spacial round-robin.
   */
  template<typename RandomAccessIterator1, typename RandomAccessIterator2, typename Pred, typename Selector>
  std::pair<RandomAccessIterator1, RandomAccessIterator2>
  find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
		RandomAccessIterator2 begin2, Pred pred, Selector selector,
		growing_blocks_tag)
  {
    _GLIBCXX_CALL(end1 - begin1)

    typedef std::iterator_traits<RandomAccessIterator1> traits_type;
    typedef typename traits_type::difference_type difference_type;
    typedef typename traits_type::value_type value_type;

    difference_type length = end1 - begin1;

    difference_type sequential_search_size = std::min<difference_type>(length, Settings::find_sequential_search_size);

    // Try it sequentially first.
    std::pair<RandomAccessIterator1, RandomAccessIterator2> find_seq_result =
      selector.sequential_algorithm(begin1, begin1 + sequential_search_size, begin2, pred);

    if (find_seq_result.first != (begin1 + sequential_search_size))
      return find_seq_result;

    // Index of beginning of next free block (after sequential find).
    difference_type next_block_pos = sequential_search_size;
    difference_type result = length;
    const thread_index_t num_threads = get_max_threads();

#pragma omp parallel shared(result) num_threads(num_threads)
    {
      // Not within first k elements -> start parallel.
      thread_index_t iam = omp_get_thread_num();

      difference_type block_size = Settings::find_initial_block_size;
      difference_type start = fetch_and_add<difference_type>(&next_block_pos, block_size);

      // Get new block, update pointer to next block.
      difference_type stop = std::min<difference_type>(length, start + block_size);

      std::pair<RandomAccessIterator1, RandomAccessIterator2> local_result;

      while (start < length)
	{
#pragma omp flush(result)
	  // Get new value of result.
	  if (result < start)
	    {
	      // No chance to find first element.
	      break;
	    }

	  local_result = selector.sequential_algorithm(begin1 + start, begin1 + stop, begin2 + start, pred);
	  if (local_result.first != (begin1 + stop))
	    {
#pragma omp critical(result)
	      if ((local_result.first - begin1) < result)
		{
		  result = local_result.first - begin1;

		  // Result cannot be in future blocks, stop algorithm.
		  fetch_and_add<difference_type>(&next_block_pos, length);
		}
	    }

	  block_size = std::min<difference_type>(block_size * Settings::find_increasing_factor, Settings::find_maximum_block_size);

	  // Get new block, update pointer to next block.
	  start = fetch_and_add<difference_type>(&next_block_pos, block_size);
	  stop = (length < (start + block_size)) ? length : (start + block_size);
	}
    }

    // Return iterator on found element.
    return std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result, begin2 + result);
  }

#endif

#if _GLIBCXX_FIND_CONSTANT_SIZE_BLOCKS

  /** 
   *   @brief Parallel std::find, constant block size variant.
   *  @param begin1 Begin iterator of first sequence.
   *  @param end1 End iterator of first sequence.
   *  @param begin2 Begin iterator of second sequence. Second sequence
   *  must have same length as first sequence.
   *  @param pred Find predicate.
   *  @param selector Functionality (e. g. std::find_if (), std::equal(),...)
   *  @return Place of finding in both sequences.
   *  @see __gnu_parallel::Settings::find_sequential_search_size
   *  @see __gnu_parallel::Settings::find_block_size
   *  There are two main differences between the growing blocks and the
   *  constant-size blocks variants.
   *  1. For GB, the block size grows; for CSB, the block size is fixed.
   *  2. For GB, the blocks are allocated dynamically; for CSB, the
   *  blocks are allocated in a predetermined manner, namely spacial
   *  round-robin.
   */
  template<typename RandomAccessIterator1, typename RandomAccessIterator2, typename Pred, typename Selector>
  std::pair<RandomAccessIterator1, RandomAccessIterator2>
  find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
		RandomAccessIterator2 begin2, Pred pred, Selector selector,
		constant_size_blocks_tag)
  {
    _GLIBCXX_CALL(end1 - begin1)
    typedef std::iterator_traits<RandomAccessIterator1> traits_type;
    typedef typename traits_type::difference_type difference_type;
    typedef typename traits_type::value_type value_type;

    difference_type length = end1 - begin1;

    difference_type sequential_search_size = std::min<difference_type>(length, Settings::find_sequential_search_size);

    // Try it sequentially first.
    std::pair<RandomAccessIterator1, RandomAccessIterator2> find_seq_result =
      selector.sequential_algorithm(begin1, begin1 + sequential_search_size, begin2, pred);

    if (find_seq_result.first != (begin1 + sequential_search_size))
      return find_seq_result;

    difference_type result = length;
    const thread_index_t num_threads = get_max_threads();

    // Not within first sequential_search_size elements -> start parallel.
#pragma omp parallel shared(result) num_threads(num_threads)
    {
      thread_index_t iam = omp_get_thread_num();
      difference_type block_size = Settings::find_initial_block_size;

      difference_type start, stop;

      // First element of thread's current iteration.
      difference_type iteration_start = sequential_search_size;

      // Where to work (initialization).
      start = iteration_start + iam * block_size;
      stop = std::min<difference_type>(length, start + block_size);

      std::pair<RandomAccessIterator1, RandomAccessIterator2> local_result;

      while (start < length)
	{
	  // Get new value of result.
#pragma omp flush(result)
	  // No chance to find first element.
	  if (result < start)
	    break;

	  local_result = selector.sequential_algorithm(begin1 + start, begin1 + stop, begin2 + start, pred);
	  if (local_result.first != (begin1 + stop))
	    {
#pragma omp critical(result)
	      if ((local_result.first - begin1) < result)
		result = local_result.first - begin1;

	      // Will not find better value in its interval.
	      break;
	    }

	  iteration_start += num_threads * block_size;

	  // Where to work.
	  start = iteration_start + iam * block_size;
	  stop = std::min<difference_type>(length, start + block_size);
	}
    }

    // Return iterator on found element.
    return std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result, begin2 + result);
  }
#endif
} // end namespace

#endif