libstdc++-v3/include/parallel/find.h - gcc - Git at Google

 // -*- C++ -*-

 // Copyright (C) 2007-2020 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 3, 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.

 // Under Section 7 of GPL version 3, you are granted additional
 // permissions described in the GCC Runtime Library Exception, version
 // 3.1, as published by the Free Software Foundation.

 // You should have received a copy of the GNU General Public License and
 // a copy of the GCC Runtime Library Exception along with this program;
 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 // <http://www.gnu.org/licenses/>.

 /** @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 _RAIter1,
 	   typename _RAIter2,
 	   typename _Pred,
            typename _Selector>
     inline std::pair<_RAIter1, _RAIter2>
     __find_template(_RAIter1 __begin1, _RAIter1 __end1,
 		    _RAIter2 __begin2, _Pred __pred, _Selector __selector)
     {
       switch (_Settings::get().find_algorithm)
 	{
 	case GROWING_BLOCKS:
           return __find_template(__begin1, __end1, __begin2, __pred,
 				 __selector, growing_blocks_tag());
 	case CONSTANT_SIZE_BLOCKS:
           return __find_template(__begin1, __end1, __begin2, __pred,
 				 __selector, constant_size_blocks_tag());
 	case 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 _RAIter1,
            typename _RAIter2,
            typename _Pred,
            typename _Selector>
     std::pair<_RAIter1, _RAIter2>
     __find_template(_RAIter1 __begin1, _RAIter1 __end1,
 		    _RAIter2 __begin2, _Pred __pred,
 		    _Selector __selector, equal_split_tag)
     {
       _GLIBCXX_CALL(__end1 - __begin1)

       typedef std::iterator_traits<_RAIter1> _TraitsType;
       typedef typename _TraitsType::difference_type _DifferenceType;
       typedef typename _TraitsType::value_type _ValueType;

       _DifferenceType __length = __end1 - __begin1;
       _DifferenceType __result = __length;
       _DifferenceType* __borders;

       omp_lock_t __result_lock;
       omp_init_lock(&__result_lock);

       _ThreadIndex __num_threads = __get_max_threads();
 #     pragma omp parallel num_threads(__num_threads)
       {
 #     pragma omp single
 	{
 	  __num_threads = omp_get_num_threads();
 	  __borders = new _DifferenceType[__num_threads + 1];
 	  __equally_split(__length, __num_threads, __borders);
 	} //single

 	_ThreadIndex __iam = omp_get_thread_num();
 	_DifferenceType __start = __borders[__iam],
 	                 __stop = __borders[__iam + 1];

 	_RAIter1 __i1 = __begin1 + __start;
 	_RAIter2 __i2 = __begin2 + __start;
 	for (_DifferenceType __pos = __start; __pos < __stop; ++__pos)
 	  {
 #           pragma omp flush(__result)
 	    // Result has been set to something lower.
 	    if (__result < __pos)
 	      break;

 	    if (__selector(__i1, __i2, __pred))
 	      {
 		omp_set_lock(&__result_lock);
 		if (__pos < __result)
 		  __result = __pos;
 		omp_unset_lock(&__result_lock);
 		break;
 	      }
 	    ++__i1;
 	    ++__i2;
 	  }
       } //parallel

       omp_destroy_lock(&__result_lock);
       delete[] __borders;

       return std::pair<_RAIter1, _RAIter2>(__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_scale_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 _RAIter1,
            typename _RAIter2,
            typename _Pred,
            typename _Selector>
     std::pair<_RAIter1, _RAIter2>
     __find_template(_RAIter1 __begin1, _RAIter1 __end1,
 		    _RAIter2 __begin2, _Pred __pred, _Selector __selector,
 		    growing_blocks_tag)
     {
       _GLIBCXX_CALL(__end1 - __begin1)

       typedef std::iterator_traits<_RAIter1> _TraitsType;
       typedef typename _TraitsType::difference_type _DifferenceType;
       typedef typename _TraitsType::value_type _ValueType;

       const _Settings& __s = _Settings::get();

       _DifferenceType __length = __end1 - __begin1;

       _DifferenceType
 	__sequential_search_size = std::min<_DifferenceType>
 	(__length, __s.find_sequential_search_size);

       // Try it sequentially first.
       std::pair<_RAIter1, _RAIter2>
 	__find_seq_result = __selector._M_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).
       _DifferenceType __next_block_start = __sequential_search_size;
       _DifferenceType __result = __length;

       omp_lock_t __result_lock;
       omp_init_lock(&__result_lock);

       const float __scale_factor = __s.find_scale_factor;

       _ThreadIndex __num_threads = __get_max_threads();
 #     pragma omp parallel shared(__result) num_threads(__num_threads)
       {
 #       pragma omp single
 	__num_threads = omp_get_num_threads();

 	// Not within first __k elements -> start parallel.
 	_ThreadIndex __iam = omp_get_thread_num();

 	_DifferenceType __block_size =
 	  std::max<_DifferenceType>(1, __scale_factor * __next_block_start);
 	_DifferenceType __start = __fetch_and_add<_DifferenceType>
 	  (&__next_block_start, __block_size);

 	// Get new block, update pointer to next block.
 	_DifferenceType __stop =
 	  std::min<_DifferenceType>(__length, __start + __block_size);

 	std::pair<_RAIter1, _RAIter2> __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._M_sequential_algorithm
 	      (__begin1 + __start, __begin1 + __stop,
 	       __begin2 + __start, __pred);

 	    if (__local_result.first != (__begin1 + __stop))
 	      {
 		omp_set_lock(&__result_lock);
 		if ((__local_result.first - __begin1) < __result)
 		  {
 		    __result = __local_result.first - __begin1;

 		    // Result cannot be in future blocks, stop algorithm.
 		    __fetch_and_add<_DifferenceType>(&__next_block_start,
 						     __length);
 		  }
 		omp_unset_lock(&__result_lock);
 	      }

 	    _DifferenceType __block_size =
 	     std::max<_DifferenceType>(1, __scale_factor * __next_block_start);

 	    // Get new block, update pointer to next block.
 	    __start = __fetch_and_add<_DifferenceType>(&__next_block_start,
 						       __block_size);
 	    __stop =
 	      std::min<_DifferenceType>(__length, __start + __block_size);
 	  }
       } //parallel

       omp_destroy_lock(&__result_lock);

       // Return iterator on found element.
       return
 	std::pair<_RAIter1, _RAIter2>(__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 _RAIter1,
            typename _RAIter2,
            typename _Pred,
            typename _Selector>
     std::pair<_RAIter1, _RAIter2>
     __find_template(_RAIter1 __begin1, _RAIter1 __end1,
                   _RAIter2 __begin2, _Pred __pred, _Selector __selector,
                   constant_size_blocks_tag)
     {
       _GLIBCXX_CALL(__end1 - __begin1)
       typedef std::iterator_traits<_RAIter1> _TraitsType;
       typedef typename _TraitsType::difference_type _DifferenceType;
       typedef typename _TraitsType::value_type _ValueType;

       const _Settings& __s = _Settings::get();

       _DifferenceType __length = __end1 - __begin1;

       _DifferenceType __sequential_search_size = std::min<_DifferenceType>
 	(__length, __s.find_sequential_search_size);

       // Try it sequentially first.
       std::pair<_RAIter1, _RAIter2>
 	__find_seq_result = __selector._M_sequential_algorithm
 	(__begin1, __begin1 + __sequential_search_size, __begin2, __pred);

       if (__find_seq_result.first != (__begin1 + __sequential_search_size))
 	return __find_seq_result;

       _DifferenceType __result = __length;
       omp_lock_t __result_lock;
       omp_init_lock(&__result_lock);

       // Not within first __sequential_search_size elements -> start parallel.

       _ThreadIndex __num_threads = __get_max_threads();
 #     pragma omp parallel shared(__result) num_threads(__num_threads)
       {
 #       pragma omp single
 	__num_threads = omp_get_num_threads();

 	_ThreadIndex __iam = omp_get_thread_num();
 	_DifferenceType __block_size = __s.find_initial_block_size;

 	// First element of thread's current iteration.
 	_DifferenceType __iteration_start = __sequential_search_size;

 	// Where to work (initialization).
 	_DifferenceType __start = __iteration_start + __iam * __block_size;
 	_DifferenceType __stop = std::min<_DifferenceType>(__length,
 							   __start
 							   + __block_size);

 	std::pair<_RAIter1, _RAIter2> __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._M_sequential_algorithm
 	      (__begin1 + __start, __begin1 + __stop,
 	       __begin2 + __start, __pred);

 	    if (__local_result.first != (__begin1 + __stop))
 	      {
 		omp_set_lock(&__result_lock);
 		if ((__local_result.first - __begin1) < __result)
 		  __result = __local_result.first - __begin1;
 		omp_unset_lock(&__result_lock);
 		// 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<_DifferenceType>(__length,
 					       __start + __block_size);
 	  }
       } //parallel

       omp_destroy_lock(&__result_lock);

       // Return iterator on found element.
       return std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
 					   __begin2 + __result);
     }
 #endif
 } // end namespace

 #endif /* _GLIBCXX_PARALLEL_FIND_H */
	// -- C++ --

	// Copyright (C) 2007-2020 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 3, 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.

	// Under Section 7 of GPL version 3, you are granted additional
	// permissions described in the GCC Runtime Library Exception, version
	// 3.1, as published by the Free Software Foundation.

	// You should have received a copy of the GNU General Public License and
	// a copy of the GCC Runtime Library Exception along with this program;
	// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
	// <http://www.gnu.org/licenses/>.

	/** @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 _RAIter1,
	typename _RAIter2,
	typename _Pred,
	typename _Selector>
	inline std::pair<_RAIter1, _RAIter2>
	__find_template(_RAIter1 __begin1, _RAIter1 __end1,
	_RAIter2 __begin2, _Pred __pred, _Selector __selector)
	{
	switch (_Settings::get().find_algorithm)
	{
	case GROWING_BLOCKS:
	return __find_template(__begin1, __end1, __begin2, __pred,
	__selector, growing_blocks_tag());
	case CONSTANT_SIZE_BLOCKS:
	return __find_template(__begin1, __end1, __begin2, __pred,
	__selector, constant_size_blocks_tag());
	case 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 _RAIter1,
	typename _RAIter2,
	typename _Pred,
	typename _Selector>
	std::pair<_RAIter1, _RAIter2>
	__find_template(_RAIter1 __begin1, _RAIter1 __end1,
	_RAIter2 __begin2, _Pred __pred,
	_Selector __selector, equal_split_tag)
	{
	_GLIBCXX_CALL(__end1 - __begin1)

	typedef std::iterator_traits<_RAIter1> _TraitsType;
	typedef typename _TraitsType::difference_type _DifferenceType;
	typedef typename _TraitsType::value_type _ValueType;

	_DifferenceType __length = __end1 - __begin1;
	_DifferenceType __result = __length;
	_DifferenceType* __borders;

	omp_lock_t __result_lock;
	omp_init_lock(&__result_lock);

	_ThreadIndex __num_threads = __get_max_threads();
	# pragma omp parallel num_threads(__num_threads)
	{
	# pragma omp single
	{
	__num_threads = omp_get_num_threads();
	__borders = new _DifferenceType[__num_threads + 1];
	__equally_split(__length, __num_threads, __borders);
	} //single

	_ThreadIndex __iam = omp_get_thread_num();
	_DifferenceType __start = __borders[__iam],
	__stop = __borders[__iam + 1];

	_RAIter1 __i1 = __begin1 + __start;
	_RAIter2 __i2 = __begin2 + __start;
	for (_DifferenceType __pos = __start; __pos < __stop; ++__pos)
	{
	# pragma omp flush(__result)
	// Result has been set to something lower.
	if (__result < __pos)
	break;

	if (__selector(__i1, __i2, __pred))
	{
	omp_set_lock(&__result_lock);
	if (__pos < __result)
	__result = __pos;
	omp_unset_lock(&__result_lock);
	break;
	}
	++__i1;
	++__i2;
	}
	} //parallel

	omp_destroy_lock(&__result_lock);
	delete[] __borders;

	return std::pair<_RAIter1, _RAIter2>(__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_scale_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 _RAIter1,
	typename _RAIter2,
	typename _Pred,
	typename _Selector>
	std::pair<_RAIter1, _RAIter2>
	__find_template(_RAIter1 __begin1, _RAIter1 __end1,
	_RAIter2 __begin2, _Pred __pred, _Selector __selector,
	growing_blocks_tag)
	{
	_GLIBCXX_CALL(__end1 - __begin1)

	typedef std::iterator_traits<_RAIter1> _TraitsType;
	typedef typename _TraitsType::difference_type _DifferenceType;
	typedef typename _TraitsType::value_type _ValueType;

	const _Settings& __s = _Settings::get();

	_DifferenceType __length = __end1 - __begin1;

	_DifferenceType
	__sequential_search_size = std::min<_DifferenceType>
	(__length, __s.find_sequential_search_size);

	// Try it sequentially first.
	std::pair<_RAIter1, _RAIter2>
	__find_seq_result = __selector._M_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).
	_DifferenceType __next_block_start = __sequential_search_size;
	_DifferenceType __result = __length;

	omp_lock_t __result_lock;
	omp_init_lock(&__result_lock);

	const float __scale_factor = __s.find_scale_factor;

	_ThreadIndex __num_threads = __get_max_threads();
	# pragma omp parallel shared(__result) num_threads(__num_threads)
	{
	# pragma omp single
	__num_threads = omp_get_num_threads();

	// Not within first __k elements -> start parallel.
	_ThreadIndex __iam = omp_get_thread_num();

	_DifferenceType __block_size =
	std::max<_DifferenceType>(1, __scale_factor * __next_block_start);
	_DifferenceType __start = __fetch_and_add<_DifferenceType>
	(&__next_block_start, __block_size);

	// Get new block, update pointer to next block.
	_DifferenceType __stop =
	std::min<_DifferenceType>(__length, __start + __block_size);

	std::pair<_RAIter1, _RAIter2> __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._M_sequential_algorithm
	(__begin1 + __start, __begin1 + __stop,
	__begin2 + __start, __pred);

	if (__local_result.first != (__begin1 + __stop))
	{
	omp_set_lock(&__result_lock);
	if ((__local_result.first - __begin1) < __result)
	{
	__result = __local_result.first - __begin1;

	// Result cannot be in future blocks, stop algorithm.
	__fetch_and_add<_DifferenceType>(&__next_block_start,
	__length);
	}
	omp_unset_lock(&__result_lock);
	}

	_DifferenceType __block_size =
	std::max<_DifferenceType>(1, __scale_factor * __next_block_start);

	// Get new block, update pointer to next block.
	__start = __fetch_and_add<_DifferenceType>(&__next_block_start,
	__block_size);
	__stop =
	std::min<_DifferenceType>(__length, __start + __block_size);
	}
	} //parallel

	omp_destroy_lock(&__result_lock);

	// Return iterator on found element.
	return
	std::pair<_RAIter1, _RAIter2>(__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 _RAIter1,
	typename _RAIter2,
	typename _Pred,
	typename _Selector>
	std::pair<_RAIter1, _RAIter2>
	__find_template(_RAIter1 __begin1, _RAIter1 __end1,
	_RAIter2 __begin2, _Pred __pred, _Selector __selector,
	constant_size_blocks_tag)
	{
	_GLIBCXX_CALL(__end1 - __begin1)
	typedef std::iterator_traits<_RAIter1> _TraitsType;
	typedef typename _TraitsType::difference_type _DifferenceType;
	typedef typename _TraitsType::value_type _ValueType;

	const _Settings& __s = _Settings::get();

	_DifferenceType __length = __end1 - __begin1;

	_DifferenceType __sequential_search_size = std::min<_DifferenceType>
	(__length, __s.find_sequential_search_size);

	// Try it sequentially first.
	std::pair<_RAIter1, _RAIter2>
	__find_seq_result = __selector._M_sequential_algorithm
	(__begin1, __begin1 + __sequential_search_size, __begin2, __pred);

	if (__find_seq_result.first != (__begin1 + __sequential_search_size))
	return __find_seq_result;

	_DifferenceType __result = __length;
	omp_lock_t __result_lock;
	omp_init_lock(&__result_lock);

	// Not within first __sequential_search_size elements -> start parallel.

	_ThreadIndex __num_threads = __get_max_threads();
	# pragma omp parallel shared(__result) num_threads(__num_threads)
	{
	# pragma omp single
	__num_threads = omp_get_num_threads();

	_ThreadIndex __iam = omp_get_thread_num();
	_DifferenceType __block_size = __s.find_initial_block_size;

	// First element of thread's current iteration.
	_DifferenceType __iteration_start = __sequential_search_size;

	// Where to work (initialization).
	_DifferenceType __start = __iteration_start + __iam * __block_size;
	_DifferenceType __stop = std::min<_DifferenceType>(__length,
	__start
	+ __block_size);

	std::pair<_RAIter1, _RAIter2> __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._M_sequential_algorithm
	(__begin1 + __start, __begin1 + __stop,
	__begin2 + __start, __pred);

	if (__local_result.first != (__begin1 + __stop))
	{
	omp_set_lock(&__result_lock);
	if ((__local_result.first - __begin1) < __result)
	__result = __local_result.first - __begin1;
	omp_unset_lock(&__result_lock);
	// 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<_DifferenceType>(__length,
	__start + __block_size);
	}
	} //parallel

	omp_destroy_lock(&__result_lock);

	// Return iterator on found element.
	return std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
	__begin2 + __result);
	}
	#endif
	} // end namespace

	#endif /* _GLIBCXX_PARALLEL_FIND_H */