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// -*- C++ -*-

// Copyright (C) 2007, 2008, 2009 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_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 _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);

      _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 = __s.find_initial_block_size;

        _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);

              }

            __block_size = std::min<_DifferenceType>

              (__block_size * __s.find_increasing_factor,

               __s.find_maximum_block_size);

            // Get new block, update pointer to next block.

            __start = __fetch_and_add<_DifferenceType>(&__next_block_start,

                                                       __block_size);

            __stop = (__length < (__start + __block_size)

                      ? __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 */