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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/random_shuffle.h
* @brief Parallel implementation of std::random_shuffle().
* This file is a GNU parallel extension to the Standard C++ Library.
*/
// Written by Johannes Singler.
#ifndef _GLIBCXX_PARALLEL_RANDOM_SHUFFLE_H
#define _GLIBCXX_PARALLEL_RANDOM_SHUFFLE_H 1
#include <limits>
#include <bits/stl_numeric.h>
#include <parallel/parallel.h>
#include <parallel/random_number.h>
namespace __gnu_parallel
{
/** @brief Type to hold the index of a bin.
*
* Since many variables of this type are allocated, it should be
* chosen as small as possible.
*/
typedef unsigned short bin_index;
/** @brief Data known to every thread participating in
__gnu_parallel::parallel_random_shuffle(). */
template<typename RandomAccessIterator>
struct DRandomShufflingGlobalData
{
typedef std::iterator_traits<RandomAccessIterator> traits_type;
typedef typename traits_type::value_type value_type;
typedef typename traits_type::difference_type difference_type;
/** @brief Begin iterator of the source. */
RandomAccessIterator& source;
/** @brief Temporary arrays for each thread. */
value_type** temporaries;
/** @brief Two-dimensional array to hold the thread-bin distribution.
*
* Dimensions (num_threads + 1) x (num_bins + 1). */
difference_type** dist;
/** @brief Start indexes of the threads' chunks. */
difference_type* starts;
/** @brief Number of the thread that will further process the
corresponding bin. */
thread_index_t* bin_proc;
/** @brief Number of bins to distribute to. */
int num_bins;
/** @brief Number of bits needed to address the bins. */
int num_bits;
/** @brief Constructor. */
DRandomShufflingGlobalData(RandomAccessIterator& _source)
: source(_source) { }
};
/** @brief Local data for a thread participating in
__gnu_parallel::parallel_random_shuffle().
*/
template<typename RandomAccessIterator, typename RandomNumberGenerator>
struct DRSSorterPU
{
/** @brief Number of threads participating in total. */
int num_threads;
/** @brief Begin index for bins taken care of by this thread. */
bin_index bins_begin;
/** @brief End index for bins taken care of by this thread. */
bin_index bins_end;
/** @brief Random seed for this thread. */
uint32 seed;
/** @brief Pointer to global data. */
DRandomShufflingGlobalData<RandomAccessIterator>* sd;
};
/** @brief Generate a random number in @c [0,2^logp).
* @param logp Logarithm (basis 2) of the upper range bound.
* @param rng Random number generator to use.
*/
template<typename RandomNumberGenerator>
inline int
random_number_pow2(int logp, RandomNumberGenerator& rng)
{ return rng.genrand_bits(logp); }
/** @brief Random shuffle code executed by each thread.
* @param pus Array of thread-local data records. */
template<typename RandomAccessIterator, typename RandomNumberGenerator>
void
parallel_random_shuffle_drs_pu(DRSSorterPU<RandomAccessIterator,
RandomNumberGenerator>* pus)
{
typedef std::iterator_traits<RandomAccessIterator> traits_type;
typedef typename traits_type::value_type value_type;
typedef typename traits_type::difference_type difference_type;
thread_index_t iam = omp_get_thread_num();
DRSSorterPU<RandomAccessIterator, RandomNumberGenerator>* d = &pus[iam];
DRandomShufflingGlobalData<RandomAccessIterator>* sd = d->sd;
// Indexing: dist[bin][processor]
difference_type length = sd->starts[iam + 1] - sd->starts[iam];
bin_index* oracles = new bin_index[length];
difference_type* dist = new difference_type[sd->num_bins + 1];
bin_index* bin_proc = new bin_index[sd->num_bins];
value_type** temporaries = new value_type*[d->num_threads];
// Compute oracles and count appearances.
for (bin_index b = 0; b < sd->num_bins + 1; ++b)
dist[b] = 0;
int num_bits = sd->num_bits;
random_number rng(d->seed);
// First main loop.
for (difference_type i = 0; i < length; ++i)
{
bin_index oracle = random_number_pow2(num_bits, rng);
oracles[i] = oracle;
// To allow prefix (partial) sum.
++(dist[oracle + 1]);
}
for (bin_index b = 0; b < sd->num_bins + 1; ++b)
sd->dist[b][iam + 1] = dist[b];
# pragma omp barrier
# pragma omp single
{
// Sum up bins, sd->dist[s + 1][d->num_threads] now contains the
// total number of items in bin s
for (bin_index s = 0; s < sd->num_bins; ++s)
__gnu_sequential::partial_sum(sd->dist[s + 1],
sd->dist[s + 1] + d->num_threads + 1,
sd->dist[s + 1]);
}
# pragma omp barrier
sequence_index_t offset = 0, global_offset = 0;
for (bin_index s = 0; s < d->bins_begin; ++s)
global_offset += sd->dist[s + 1][d->num_threads];
# pragma omp barrier
for (bin_index s = d->bins_begin; s < d->bins_end; ++s)
{
for (int t = 0; t < d->num_threads + 1; ++t)
sd->dist[s + 1][t] += offset;
offset = sd->dist[s + 1][d->num_threads];
}
sd->temporaries[iam] = static_cast<value_type*>(
::operator new(sizeof(value_type) * offset));
# pragma omp barrier
// Draw local copies to avoid false sharing.
for (bin_index b = 0; b < sd->num_bins + 1; ++b)
dist[b] = sd->dist[b][iam];
for (bin_index b = 0; b < sd->num_bins; ++b)
bin_proc[b] = sd->bin_proc[b];
for (thread_index_t t = 0; t < d->num_threads; ++t)
temporaries[t] = sd->temporaries[t];
RandomAccessIterator source = sd->source;
difference_type start = sd->starts[iam];
// Distribute according to oracles, second main loop.
for (difference_type i = 0; i < length; ++i)
{
bin_index target_bin = oracles[i];
thread_index_t target_p = bin_proc[target_bin];
// Last column [d->num_threads] stays unchanged.
::new(&(temporaries[target_p][dist[target_bin + 1]++]))
value_type(*(source + i + start));
}
delete[] oracles;
delete[] dist;
delete[] bin_proc;
delete[] temporaries;
# pragma omp barrier
// Shuffle bins internally.
for (bin_index b = d->bins_begin; b < d->bins_end; ++b)
{
value_type* begin =
sd->temporaries[iam] +
((b == d->bins_begin) ? 0 : sd->dist[b][d->num_threads]),
* end =
sd->temporaries[iam] + sd->dist[b + 1][d->num_threads];
sequential_random_shuffle(begin, end, rng);
std::copy(begin, end, sd->source + global_offset +
((b == d->bins_begin) ? 0 : sd->dist[b][d->num_threads]));
}
::operator delete(sd->temporaries[iam]);
}
/** @brief Round up to the next greater power of 2.
* @param x Integer to round up */
template<typename T>
T
round_up_to_pow2(T x)
{
if (x <= 1)
return 1;
else
return (T)1 << (__log2(x - 1) + 1);
}
/** @brief Main parallel random shuffle step.
* @param begin Begin iterator of sequence.
* @param end End iterator of sequence.
* @param n Length of sequence.
* @param num_threads Number of threads to use.
* @param rng Random number generator to use.
*/
template<typename RandomAccessIterator, typename RandomNumberGenerator>
void
parallel_random_shuffle_drs(RandomAccessIterator begin,
RandomAccessIterator end,
typename std::iterator_traits
<RandomAccessIterator>::difference_type n,
thread_index_t num_threads,
RandomNumberGenerator& rng)
{
typedef std::iterator_traits<RandomAccessIterator> traits_type;
typedef typename traits_type::value_type value_type;
typedef typename traits_type::difference_type difference_type;
_GLIBCXX_CALL(n)
const _Settings& __s = _Settings::get();
if (num_threads > n)
num_threads = static_cast<thread_index_t>(n);
bin_index num_bins, num_bins_cache;
#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_L1
// Try the L1 cache first.
// Must fit into L1.
num_bins_cache = std::max<difference_type>(
1, n / (__s.L1_cache_size_lb / sizeof(value_type)));
num_bins_cache = round_up_to_pow2(num_bins_cache);
// No more buckets than TLB entries, power of 2
// Power of 2 and at least one element per bin, at most the TLB size.
num_bins = std::min<difference_type>(n, num_bins_cache);
#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_TLB
// 2 TLB entries needed per bin.
num_bins = std::min<difference_type>(__s.TLB_size / 2, num_bins);
#endif
num_bins = round_up_to_pow2(num_bins);
if (num_bins < num_bins_cache)
{
#endif
// Now try the L2 cache
// Must fit into L2
num_bins_cache = static_cast<bin_index>(std::max<difference_type>(
1, n / (__s.L2_cache_size / sizeof(value_type))));
num_bins_cache = round_up_to_pow2(num_bins_cache);
// No more buckets than TLB entries, power of 2.
num_bins = static_cast<bin_index>(
std::min(n, static_cast<difference_type>(num_bins_cache)));
// Power of 2 and at least one element per bin, at most the TLB size.
#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_TLB
// 2 TLB entries needed per bin.
num_bins = std::min(
static_cast<difference_type>(__s.TLB_size / 2), num_bins);
#endif
num_bins = round_up_to_pow2(num_bins);
#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_L1
}
#endif
num_threads = std::min<bin_index>(num_threads, num_bins);
if (num_threads <= 1)
return sequential_random_shuffle(begin, end, rng);
DRandomShufflingGlobalData<RandomAccessIterator> sd(begin);
DRSSorterPU<RandomAccessIterator, random_number >* pus;
difference_type* starts;
# pragma omp parallel num_threads(num_threads)
{
thread_index_t num_threads = omp_get_num_threads();
# pragma omp single
{
pus = new DRSSorterPU<RandomAccessIterator, random_number>
[num_threads];
sd.temporaries = new value_type*[num_threads];
sd.dist = new difference_type*[num_bins + 1];
sd.bin_proc = new thread_index_t[num_bins];
for (bin_index b = 0; b < num_bins + 1; ++b)
sd.dist[b] = new difference_type[num_threads + 1];
for (bin_index b = 0; b < (num_bins + 1); ++b)
{
sd.dist[0][0] = 0;
sd.dist[b][0] = 0;
}
starts = sd.starts = new difference_type[num_threads + 1];
int bin_cursor = 0;
sd.num_bins = num_bins;
sd.num_bits = __log2(num_bins);
difference_type chunk_length = n / num_threads,
split = n % num_threads, start = 0;
difference_type bin_chunk_length = num_bins / num_threads,
bin_split = num_bins % num_threads;
for (thread_index_t i = 0; i < num_threads; ++i)
{
starts[i] = start;
start += (i < split) ? (chunk_length + 1) : chunk_length;
int j = pus[i].bins_begin = bin_cursor;
// Range of bins for this processor.
bin_cursor += (i < bin_split) ?
(bin_chunk_length + 1) : bin_chunk_length;
pus[i].bins_end = bin_cursor;
for (; j < bin_cursor; ++j)
sd.bin_proc[j] = i;
pus[i].num_threads = num_threads;
pus[i].seed = rng(std::numeric_limits<uint32>::max());
pus[i].sd = &sd;
}
starts[num_threads] = start;
} //single
// Now shuffle in parallel.
parallel_random_shuffle_drs_pu(pus);
} // parallel
delete[] starts;
delete[] sd.bin_proc;
for (int s = 0; s < (num_bins + 1); ++s)
delete[] sd.dist[s];
delete[] sd.dist;
delete[] sd.temporaries;
delete[] pus;
}
/** @brief Sequential cache-efficient random shuffle.
* @param begin Begin iterator of sequence.
* @param end End iterator of sequence.
* @param rng Random number generator to use.
*/
template<typename RandomAccessIterator, typename RandomNumberGenerator>
void
sequential_random_shuffle(RandomAccessIterator begin,
RandomAccessIterator end,
RandomNumberGenerator& rng)
{
typedef std::iterator_traits<RandomAccessIterator> traits_type;
typedef typename traits_type::value_type value_type;
typedef typename traits_type::difference_type difference_type;
difference_type n = end - begin;
const _Settings& __s = _Settings::get();
bin_index num_bins, num_bins_cache;
#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_L1
// Try the L1 cache first, must fit into L1.
num_bins_cache =
std::max<difference_type>
(1, n / (__s.L1_cache_size_lb / sizeof(value_type)));
num_bins_cache = round_up_to_pow2(num_bins_cache);
// No more buckets than TLB entries, power of 2
// Power of 2 and at least one element per bin, at most the TLB size
num_bins = std::min(n, (difference_type)num_bins_cache);
#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_TLB
// 2 TLB entries needed per bin
num_bins = std::min((difference_type)__s.TLB_size / 2, num_bins);
#endif
num_bins = round_up_to_pow2(num_bins);
if (num_bins < num_bins_cache)
{
#endif
// Now try the L2 cache, must fit into L2.
num_bins_cache =
static_cast<bin_index>(std::max<difference_type>(
1, n / (__s.L2_cache_size / sizeof(value_type))));
num_bins_cache = round_up_to_pow2(num_bins_cache);
// No more buckets than TLB entries, power of 2
// Power of 2 and at least one element per bin, at most the TLB size.
num_bins = static_cast<bin_index>
(std::min(n, static_cast<difference_type>(num_bins_cache)));
#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_TLB
// 2 TLB entries needed per bin
num_bins =
std::min<difference_type>(__s.TLB_size / 2, num_bins);
#endif
num_bins = round_up_to_pow2(num_bins);
#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_L1
}
#endif
int num_bits = __log2(num_bins);
if (num_bins > 1)
{
value_type* target = static_cast<value_type*>(
::operator new(sizeof(value_type) * n));
bin_index* oracles = new bin_index[n];
difference_type* dist0 = new difference_type[num_bins + 1],
* dist1 = new difference_type[num_bins + 1];
for (int b = 0; b < num_bins + 1; ++b)
dist0[b] = 0;
random_number bitrng(rng(0xFFFFFFFF));
for (difference_type i = 0; i < n; ++i)
{
bin_index oracle = random_number_pow2(num_bits, bitrng);
oracles[i] = oracle;
// To allow prefix (partial) sum.
++(dist0[oracle + 1]);
}
// Sum up bins.
__gnu_sequential::partial_sum(dist0, dist0 + num_bins + 1, dist0);
for (int b = 0; b < num_bins + 1; ++b)
dist1[b] = dist0[b];
// Distribute according to oracles.
for (difference_type i = 0; i < n; ++i)
::new(&(target[(dist0[oracles[i]])++])) value_type(*(begin + i));
for (int b = 0; b < num_bins; ++b)
{
sequential_random_shuffle(target + dist1[b],
target + dist1[b + 1],
rng);
}
// Copy elements back.
std::copy(target, target + n, begin);
delete[] dist0;
delete[] dist1;
delete[] oracles;
::operator delete(target);
}
else
__gnu_sequential::random_shuffle(begin, end, rng);
}
/** @brief Parallel random public call.
* @param begin Begin iterator of sequence.
* @param end End iterator of sequence.
* @param rng Random number generator to use.
*/
template<typename RandomAccessIterator, typename RandomNumberGenerator>
inline void
parallel_random_shuffle(RandomAccessIterator begin,
RandomAccessIterator end,
RandomNumberGenerator rng = random_number())
{
typedef std::iterator_traits<RandomAccessIterator> traits_type;
typedef typename traits_type::difference_type difference_type;
difference_type n = end - begin;
parallel_random_shuffle_drs(begin, end, n, get_max_threads(), rng) ;
}
}
#endif /* _GLIBCXX_PARALLEL_RANDOM_SHUFFLE_H */
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