11.2.0/parallel/find.h

// -*- C++ -*-

// Copyright (C) 2007-2021 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 */
Revision:	1166
Committed:	Tue Oct 26 14:22:36 2021 UTC (4 years ago) by rossy
Content type:	text/x-chdr
File size:	13591 byte(s)
Log Message:	Daodan: Replace MinGW build env with an up-to-date MSYS2 env
#	Content
1	// -- C++ --
2
3	// Copyright (C) 2007-2021 Free Software Foundation, Inc.
4	//
5	// This file is part of the GNU ISO C++ Library. This library is free
6	// software; you can redistribute it and/or modify it under the terms
7	// of the GNU General Public License as published by the Free Software
8	// Foundation; either version 3, or (at your option) any later
9	// version.
10
11	// This library is distributed in the hope that it will be useful, but
12	// WITHOUT ANY WARRANTY; without even the implied warranty of
13	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14	// General Public License for more details.
15
16	// Under Section 7 of GPL version 3, you are granted additional
17	// permissions described in the GCC Runtime Library Exception, version
18	// 3.1, as published by the Free Software Foundation.
19
20	// You should have received a copy of the GNU General Public License and
21	// a copy of the GCC Runtime Library Exception along with this program;
22	// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23	// <http://www.gnu.org/licenses/>.
24
25	/** @file parallel/find.h
26	* @brief Parallel implementation base for std::find(), std::equal()
27	* and related functions.
28	* This file is a GNU parallel extension to the Standard C++ Library.
29	*/
30
31	// Written by Felix Putze and Johannes Singler.
32
33	#ifndef _GLIBCXX_PARALLEL_FIND_H
34	#define _GLIBCXX_PARALLEL_FIND_H 1
35
36	#include <bits/stl_algobase.h>
37
38	#include <parallel/features.h>
39	#include <parallel/parallel.h>
40	#include <parallel/compatibility.h>
41	#include <parallel/equally_split.h>
42
43	namespace __gnu_parallel
44	{
45	/**
46	* @brief Parallel std::find, switch for different algorithms.
47	* @param __begin1 Begin iterator of first sequence.
48	* @param __end1 End iterator of first sequence.
49	* @param __begin2 Begin iterator of second sequence. Must have same
50	* length as first sequence.
51	* @param __pred Find predicate.
52	* @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
53	* @return Place of finding in both sequences.
54	*/
55	template<typename _RAIter1,
56	typename _RAIter2,
57	typename _Pred,
58	typename _Selector>
59	inline std::pair<_RAIter1, _RAIter2>
60	__find_template(_RAIter1 __begin1, _RAIter1 __end1,
61	_RAIter2 __begin2, _Pred __pred, _Selector __selector)
62	{
63	switch (_Settings::get().find_algorithm)
64	{
65	case GROWING_BLOCKS:
66	return __find_template(__begin1, __end1, __begin2, __pred,
67	__selector, growing_blocks_tag());
68	case CONSTANT_SIZE_BLOCKS:
69	return __find_template(__begin1, __end1, __begin2, __pred,
70	__selector, constant_size_blocks_tag());
71	case EQUAL_SPLIT:
72	return __find_template(__begin1, __end1, __begin2, __pred,
73	__selector, equal_split_tag());
74	default:
75	_GLIBCXX_PARALLEL_ASSERT(false);
76	return std::make_pair(__begin1, __begin2);
77	}
78	}
79
80	#if _GLIBCXX_FIND_EQUAL_SPLIT
81
82	/**
83	* @brief Parallel std::find, equal splitting variant.
84	* @param __begin1 Begin iterator of first sequence.
85	* @param __end1 End iterator of first sequence.
86	* @param __begin2 Begin iterator of second sequence. Second __sequence
87	* must have same length as first sequence.
88	* @param __pred Find predicate.
89	* @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
90	* @return Place of finding in both sequences.
91	*/
92	template<typename _RAIter1,
93	typename _RAIter2,
94	typename _Pred,
95	typename _Selector>
96	std::pair<_RAIter1, _RAIter2>
97	__find_template(_RAIter1 __begin1, _RAIter1 __end1,
98	_RAIter2 __begin2, _Pred __pred,
99	_Selector __selector, equal_split_tag)
100	{
101	_GLIBCXX_CALL(__end1 - __begin1)
102
103	typedef std::iterator_traits<_RAIter1> _TraitsType;
104	typedef typename _TraitsType::difference_type _DifferenceType;
105	typedef typename _TraitsType::value_type _ValueType;
106
107	_DifferenceType __length = __end1 - __begin1;
108	_DifferenceType __result = __length;
109	_DifferenceType* __borders;
110
111	omp_lock_t __result_lock;
112	omp_init_lock(&__result_lock);
113
114	_ThreadIndex __num_threads = __get_max_threads();
115	# pragma omp parallel num_threads(__num_threads)
116	{
117	# pragma omp single
118	{
119	__num_threads = omp_get_num_threads();
120	__borders = new _DifferenceType[__num_threads + 1];
121	__equally_split(__length, __num_threads, __borders);
122	} //single
123
124	_ThreadIndex __iam = omp_get_thread_num();
125	_DifferenceType __start = __borders[__iam],
126	__stop = __borders[__iam + 1];
127
128	_RAIter1 __i1 = __begin1 + __start;
129	_RAIter2 __i2 = __begin2 + __start;
130	for (_DifferenceType __pos = __start; __pos < __stop; ++__pos)
131	{
132	# pragma omp flush(__result)
133	// Result has been set to something lower.
134	if (__result < __pos)
135	break;
136
137	if (__selector(__i1, __i2, __pred))
138	{
139	omp_set_lock(&__result_lock);
140	if (__pos < __result)
141	__result = __pos;
142	omp_unset_lock(&__result_lock);
143	break;
144	}
145	++__i1;
146	++__i2;
147	}
148	} //parallel
149
150	omp_destroy_lock(&__result_lock);
151	delete[] __borders;
152
153	return std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
154	__begin2 + __result);
155	}
156
157	#endif
158
159	#if _GLIBCXX_FIND_GROWING_BLOCKS
160
161	/**
162	* @brief Parallel std::find, growing block size variant.
163	* @param __begin1 Begin iterator of first sequence.
164	* @param __end1 End iterator of first sequence.
165	* @param __begin2 Begin iterator of second sequence. Second __sequence
166	* must have same length as first sequence.
167	* @param __pred Find predicate.
168	* @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
169	* @return Place of finding in both sequences.
170	* @see __gnu_parallel::_Settings::find_sequential_search_size
171	* @see __gnu_parallel::_Settings::find_scale_factor
172	*
173	* There are two main differences between the growing blocks and
174	* the constant-size blocks variants.
175	* 1. For GB, the block size grows; for CSB, the block size is fixed.
176	* 2. For GB, the blocks are allocated dynamically;
177	* for CSB, the blocks are allocated in a predetermined manner,
178	* namely spacial round-robin.
179	*/
180	template<typename _RAIter1,
181	typename _RAIter2,
182	typename _Pred,
183	typename _Selector>
184	std::pair<_RAIter1, _RAIter2>
185	__find_template(_RAIter1 __begin1, _RAIter1 __end1,
186	_RAIter2 __begin2, _Pred __pred, _Selector __selector,
187	growing_blocks_tag)
188	{
189	_GLIBCXX_CALL(__end1 - __begin1)
190
191	typedef std::iterator_traits<_RAIter1> _TraitsType;
192	typedef typename _TraitsType::difference_type _DifferenceType;
193	typedef typename _TraitsType::value_type _ValueType;
194
195	const _Settings& __s = _Settings::get();
196
197	_DifferenceType __length = __end1 - __begin1;
198
199	_DifferenceType
200	__sequential_search_size = std::min<_DifferenceType>
201	(__length, __s.find_sequential_search_size);
202
203	// Try it sequentially first.
204	std::pair<_RAIter1, _RAIter2>
205	__find_seq_result = __selector._M_sequential_algorithm
206	(__begin1, __begin1 + __sequential_search_size,
207	__begin2, __pred);
208
209	if (__find_seq_result.first != (__begin1 + __sequential_search_size))
210	return __find_seq_result;
211
212	// Index of beginning of next free block (after sequential find).
213	_DifferenceType __next_block_start = __sequential_search_size;
214	_DifferenceType __result = __length;
215
216	omp_lock_t __result_lock;
217	omp_init_lock(&__result_lock);
218
219	const float __scale_factor = __s.find_scale_factor;
220
221	_ThreadIndex __num_threads = __get_max_threads();
222	# pragma omp parallel shared(__result) num_threads(__num_threads)
223	{
224	# pragma omp single
225	__num_threads = omp_get_num_threads();
226
227	// Not within first __k elements -> start parallel.
228	_ThreadIndex __iam = omp_get_thread_num();
229
230	_DifferenceType __block_size =
231	std::max<_DifferenceType>(1, __scale_factor * __next_block_start);
232	_DifferenceType __start = __fetch_and_add<_DifferenceType>
233	(&__next_block_start, __block_size);
234
235	// Get new block, update pointer to next block.
236	_DifferenceType __stop =
237	std::min<_DifferenceType>(__length, __start + __block_size);
238
239	std::pair<_RAIter1, _RAIter2> __local_result;
240
241	while (__start < __length)
242	{
243	# pragma omp flush(__result)
244	// Get new value of result.
245	if (__result < __start)
246	{
247	// No chance to find first element.
248	break;
249	}
250
251	__local_result = __selector._M_sequential_algorithm
252	(__begin1 + __start, __begin1 + __stop,
253	__begin2 + __start, __pred);
254
255	if (__local_result.first != (__begin1 + __stop))
256	{
257	omp_set_lock(&__result_lock);
258	if ((__local_result.first - __begin1) < __result)
259	{
260	__result = __local_result.first - __begin1;
261
262	// Result cannot be in future blocks, stop algorithm.
263	__fetch_and_add<_DifferenceType>(&__next_block_start,
264	__length);
265	}
266	omp_unset_lock(&__result_lock);
267	}
268
269	_DifferenceType __block_size =
270	std::max<_DifferenceType>(1, __scale_factor * __next_block_start);
271
272	// Get new block, update pointer to next block.
273	__start = __fetch_and_add<_DifferenceType>(&__next_block_start,
274	__block_size);
275	__stop =
276	std::min<_DifferenceType>(__length, __start + __block_size);
277	}
278	} //parallel
279
280	omp_destroy_lock(&__result_lock);
281
282	// Return iterator on found element.
283	return
284	std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
285	__begin2 + __result);
286	}
287
288	#endif
289
290	#if _GLIBCXX_FIND_CONSTANT_SIZE_BLOCKS
291
292	/**
293	* @brief Parallel std::find, constant block size variant.
294	* @param __begin1 Begin iterator of first sequence.
295	* @param __end1 End iterator of first sequence.
296	* @param __begin2 Begin iterator of second sequence. Second __sequence
297	* must have same length as first sequence.
298	* @param __pred Find predicate.
299	* @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
300	* @return Place of finding in both sequences.
301	* @see __gnu_parallel::_Settings::find_sequential_search_size
302	* @see __gnu_parallel::_Settings::find_block_size
303	* There are two main differences between the growing blocks and the
304	* constant-size blocks variants.
305	* 1. For GB, the block size grows; for CSB, the block size is fixed.
306	* 2. For GB, the blocks are allocated dynamically; for CSB, the
307	* blocks are allocated in a predetermined manner, namely spacial
308	* round-robin.
309	*/
310	template<typename _RAIter1,
311	typename _RAIter2,
312	typename _Pred,
313	typename _Selector>
314	std::pair<_RAIter1, _RAIter2>
315	__find_template(_RAIter1 __begin1, _RAIter1 __end1,
316	_RAIter2 __begin2, _Pred __pred, _Selector __selector,
317	constant_size_blocks_tag)
318	{
319	_GLIBCXX_CALL(__end1 - __begin1)
320	typedef std::iterator_traits<_RAIter1> _TraitsType;
321	typedef typename _TraitsType::difference_type _DifferenceType;
322	typedef typename _TraitsType::value_type _ValueType;
323
324	const _Settings& __s = _Settings::get();
325
326	_DifferenceType __length = __end1 - __begin1;
327
328	_DifferenceType __sequential_search_size = std::min<_DifferenceType>
329	(__length, __s.find_sequential_search_size);
330
331	// Try it sequentially first.
332	std::pair<_RAIter1, _RAIter2>
333	__find_seq_result = __selector._M_sequential_algorithm
334	(__begin1, __begin1 + __sequential_search_size, __begin2, __pred);
335
336	if (__find_seq_result.first != (__begin1 + __sequential_search_size))
337	return __find_seq_result;
338
339	_DifferenceType __result = __length;
340	omp_lock_t __result_lock;
341	omp_init_lock(&__result_lock);
342
343	// Not within first __sequential_search_size elements -> start parallel.
344
345	_ThreadIndex __num_threads = __get_max_threads();
346	# pragma omp parallel shared(__result) num_threads(__num_threads)
347	{
348	# pragma omp single
349	__num_threads = omp_get_num_threads();
350
351	_ThreadIndex __iam = omp_get_thread_num();
352	_DifferenceType __block_size = __s.find_initial_block_size;
353
354	// First element of thread's current iteration.
355	_DifferenceType __iteration_start = __sequential_search_size;
356
357	// Where to work (initialization).
358	_DifferenceType __start = __iteration_start + __iam * __block_size;
359	_DifferenceType __stop = std::min<_DifferenceType>(__length,
360	__start
361	+ __block_size);
362
363	std::pair<_RAIter1, _RAIter2> __local_result;
364
365	while (__start < __length)
366	{
367	// Get new value of result.
368	# pragma omp flush(__result)
369	// No chance to find first element.
370	if (__result < __start)
371	break;
372
373	__local_result = __selector._M_sequential_algorithm
374	(__begin1 + __start, __begin1 + __stop,
375	__begin2 + __start, __pred);
376
377	if (__local_result.first != (__begin1 + __stop))
378	{
379	omp_set_lock(&__result_lock);
380	if ((__local_result.first - __begin1) < __result)
381	__result = __local_result.first - __begin1;
382	omp_unset_lock(&__result_lock);
383	// Will not find better value in its interval.
384	break;
385	}
386
387	__iteration_start += __num_threads * __block_size;
388
389	// Where to work.
390	__start = __iteration_start + __iam * __block_size;
391	__stop = std::min<_DifferenceType>(__length,
392	__start + __block_size);
393	}
394	} //parallel
395
396	omp_destroy_lock(&__result_lock);
397
398	// Return iterator on found element.
399	return std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
400	__begin2 + __result);
401	}
402	#endif
403	} // end namespace
404
405	#endif /* _GLIBCXX_PARALLEL_FIND_H */