1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
|
// -*- C++ -*-
// Copyright (C) 2007-2014 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/list_partition.h
* @brief _Functionality to split __sequence referenced by only input
* iterators.
* This file is a GNU parallel extension to the Standard C++ Library.
*/
// Written by Leonor Frias Moya and Johannes Singler.
#ifndef _GLIBCXX_PARALLEL_LIST_PARTITION_H
#define _GLIBCXX_PARALLEL_LIST_PARTITION_H 1
#include <parallel/parallel.h>
#include <vector>
namespace __gnu_parallel
{
/** @brief Shrinks and doubles the ranges.
* @param __os_starts Start positions worked on (oversampled).
* @param __count_to_two Counts up to 2.
* @param __range_length Current length of a chunk.
* @param __make_twice Whether the @c __os_starts is allowed to be
* grown or not
*/
template<typename _IIter>
void
__shrink_and_double(std::vector<_IIter>& __os_starts,
size_t& __count_to_two, size_t& __range_length,
const bool __make_twice)
{
++__count_to_two;
if (!__make_twice || __count_to_two < 2)
__shrink(__os_starts, __count_to_two, __range_length);
else
{
__os_starts.resize((__os_starts.size() - 1) * 2 + 1);
__count_to_two = 0;
}
}
/** @brief Combines two ranges into one and thus halves the number of ranges.
* @param __os_starts Start positions worked on (oversampled).
* @param __count_to_two Counts up to 2.
* @param __range_length Current length of a chunk. */
template<typename _IIter>
void
__shrink(std::vector<_IIter>& __os_starts, size_t& __count_to_two,
size_t& __range_length)
{
for (typename std::vector<_IIter>::size_type __i = 0;
__i <= (__os_starts.size() / 2); ++__i)
__os_starts[__i] = __os_starts[__i * 2];
__range_length *= 2;
}
/** @brief Splits a sequence given by input iterators into parts of
* almost equal size
*
* The function needs only one pass over the sequence.
* @param __begin Begin iterator of input sequence.
* @param __end End iterator of input sequence.
* @param __starts Start iterators for the resulting parts, dimension
* @c __num_parts+1. For convenience, @c __starts @c [__num_parts]
* contains the end iterator of the sequence.
* @param __lengths Length of the resulting parts.
* @param __num_parts Number of parts to split the sequence into.
* @param __f Functor to be applied to each element by traversing __it
* @param __oversampling Oversampling factor. If 0, then the
* partitions will differ in at most
* \sqrt{\mathrm{__end} - \mathrm{__begin}}
* __elements. Otherwise, the ratio between the
* longest and the shortest part is bounded by
* 1/(\mathrm{__oversampling} \cdot \mathrm{num\_parts})
* @return Length of the whole sequence.
*/
template<typename _IIter, typename _FunctorType>
size_t
list_partition(const _IIter __begin, const _IIter __end,
_IIter* __starts, size_t* __lengths, const int __num_parts,
_FunctorType& __f, int __oversampling = 0)
{
bool __make_twice = false;
// The resizing algorithm is chosen according to the oversampling factor.
if (__oversampling == 0)
{
__make_twice = true;
__oversampling = 1;
}
std::vector<_IIter> __os_starts(2 * __oversampling * __num_parts + 1);
__os_starts[0] = __begin;
_IIter __prev = __begin, __it = __begin;
size_t __dist_limit = 0, __dist = 0;
size_t __cur = 1, __next = 1;
size_t __range_length = 1;
size_t __count_to_two = 0;
while (__it != __end)
{
__cur = __next;
for (; __cur < __os_starts.size() and __it != __end; ++__cur)
{
for (__dist_limit += __range_length;
__dist < __dist_limit and __it != __end; ++__dist)
{
__f(__it);
++__it;
}
__os_starts[__cur] = __it;
}
// Must compare for end and not __cur < __os_starts.size() , because
// __cur could be == __os_starts.size() as well
if (__it == __end)
break;
__shrink_and_double(__os_starts, __count_to_two, __range_length,
__make_twice);
__next = __os_starts.size() / 2 + 1;
}
// Calculation of the parts (one must be extracted from __current
// because the partition beginning at end, consists only of
// itself).
size_t __size_part = (__cur - 1) / __num_parts;
int __size_greater = static_cast<int>((__cur - 1) % __num_parts);
__starts[0] = __os_starts[0];
size_t __index = 0;
// Smallest partitions.
for (int __i = 1; __i < (__num_parts + 1 - __size_greater); ++__i)
{
__lengths[__i - 1] = __size_part * __range_length;
__index += __size_part;
__starts[__i] = __os_starts[__index];
}
// Biggest partitions.
for (int __i = __num_parts + 1 - __size_greater; __i <= __num_parts;
++__i)
{
__lengths[__i - 1] = (__size_part+1) * __range_length;
__index += (__size_part+1);
__starts[__i] = __os_starts[__index];
}
// Correction of the end size (the end iteration has not finished).
__lengths[__num_parts - 1] -= (__dist_limit - __dist);
return __dist;
}
}
#endif /* _GLIBCXX_PARALLEL_LIST_PARTITION_H */
|
