include/stxxl/bits/algo/losertree.h

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/***************************************************************************
 *  include/stxxl/bits/algo/losertree.h
 *
 *  Part of the STXXL. See http://stxxl.sourceforge.net
 *
 *  Copyright (C) 1999 Peter Sanders <sanders@mpi-sb.mpg.de>
 *  Copyright (C) 2002 Roman Dementiev <dementiev@mpi-sb.mpg.de>
 *  Copyright (C) 2009 Andreas Beckmann <beckmann@cs.uni-frankfurt.de>
 *
 *  Distributed under the Boost Software License, Version 1.0.
 *  (See accompanying file LICENSE_1_0.txt or copy at
 *  http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

#ifndef STXXL_LOSERTREE_HEADER
#define STXXL_LOSERTREE_HEADER

#include <algorithm>
#include <stxxl/bits/noncopyable.h>
#include <stxxl/bits/common/utils.h>
#include <stxxl/bits/verbose.h>


__STXXL_BEGIN_NAMESPACE

template <typename run_cursor_type,
          typename run_cursor_cmp_type>
class loser_tree : private noncopyable
{
    int logK;
    int_type k;
    int_type * entry;
    run_cursor_type * current;
    run_cursor_cmp_type cmp;

    int_type init_winner(int_type root)
    {
        if (root >= k)
        {
            return root - k;
        }
        else
        {
            int_type left = init_winner(2 * root);
            int_type right = init_winner(2 * root + 1);
            if (cmp(current[left], current[right]))
            {
                entry[root] = right;
                return left;
            }
            else
            {
                entry[root] = left;
                return right;
            }
        }
    }

public:
    typedef typename run_cursor_type::prefetcher_type prefetcher_type;
    typedef typename run_cursor_type::value_type value_type;

    loser_tree(
        prefetcher_type * p,
        int_type nruns,
        run_cursor_cmp_type c) : cmp(c)
    {
        int_type i;
        logK = log2_ceil(nruns);
        int_type kReg = k = (1 << logK);

        STXXL_VERBOSE2("loser_tree: logK=" << logK << " nruns=" << nruns << " K=" << kReg);

#ifdef STXXL_SORT_SINGLE_PREFETCHER
        current = new run_cursor_type[kReg];
        run_cursor_type::set_prefetcher(p);
#else
        current = new run_cursor_type[kReg];
        for (i = 0; i < kReg; ++i)
            current[i].prefetcher() = p;
#endif
        entry = new int_type[(kReg << 1)];
        // init cursors
        for (i = 0; i < nruns; ++i)
        {
            current[i].buffer = p->pull_block();
            //current[i].pos = 0; // done in constructor
            entry[kReg + i] = i;
        }

        for (i = nruns; i < kReg; ++i)
        {
            current[i].make_inf();
            entry[kReg + i] = i;
        }

        entry[0] = init_winner(1);
    }
    ~loser_tree()
    {
        delete[] current;
        delete[] entry;
    }

    void swap(loser_tree & obj)
    {
        std::swap(logK, obj.logK);
        std::swap(k, obj.k);
        std::swap(entry, obj.entry);
        std::swap(current, obj.current);
        std::swap(cmp, obj.cmp);
    }

private:
    template <unsigned LogK>
    void multi_merge_unrolled(value_type * out_first, value_type * out_last)
    {
        run_cursor_type * currentE, * winnerE;
        int_type * regEntry = entry;
        int_type winnerIndex = regEntry[0];

        while (LIKELY(out_first != out_last))
        {
            winnerE = current + winnerIndex;
            *(out_first) = winnerE->current();
            ++out_first;

            ++(*winnerE);


#define TreeStep(L) \
    if (LogK >= L) \
    { \
        currentE = current + \
                   regEntry[(winnerIndex + (1 << LogK)) >> (((int(LogK - L) + 1) >= 0) ? ((LogK - L) + 1) : 0)]; \
        if (cmp(*currentE, *winnerE)) \
        { \
            std::swap(regEntry[(winnerIndex + (1 << LogK)) \
                               >> (((int(LogK - L) + 1) >= 0) ? ((LogK - L) + 1) : 0)], winnerIndex); \
            winnerE = currentE; \
        } \
    }

            TreeStep(10);
            TreeStep(9);
            TreeStep(8);
            TreeStep(7);
            TreeStep(6);
            TreeStep(5);
            TreeStep(4);
            TreeStep(3);
            TreeStep(2);
            TreeStep(1);

#undef TreeStep
        }

        regEntry[0] = winnerIndex;
    }

    void multi_merge_unrolled_0(value_type * out_first, value_type * out_last)
    {
        while (LIKELY(out_first != out_last))
        {
            *out_first = current->current();
            ++out_first;
            ++(*current);
        }
    }

    void multi_merge_k(value_type * out_first, value_type * out_last)
    {
        run_cursor_type * currentE, * winnerE;
        int_type kReg = k;
        int_type winnerIndex = entry[0];

        while (LIKELY(out_first != out_last))
        {
            winnerE = current + winnerIndex;
            *(out_first) = winnerE->current();
            ++out_first;

            ++(*winnerE);

            for (int_type i = (winnerIndex + kReg) >> 1; i > 0; i >>= 1)
            {
                currentE = current + entry[i];

                if (cmp(*currentE, *winnerE))
                {
                    std::swap(entry[i], winnerIndex);
                    winnerE = currentE;
                }
            }
        }

        entry[0] = winnerIndex;
    }

public:
    void multi_merge(value_type * out_first, value_type * out_last)
    {
        switch (logK)
        {
        case 0:
            multi_merge_unrolled_0(out_first, out_last);
            break;
        case 1:
            multi_merge_unrolled<1>(out_first, out_last);
            break;
        case 2:
            multi_merge_unrolled<2>(out_first, out_last);
            break;
        case 3:
            multi_merge_unrolled<3>(out_first, out_last);
            break;
        case 4:
            multi_merge_unrolled<4>(out_first, out_last);
            break;
        case 5:
            multi_merge_unrolled<5>(out_first, out_last);
            break;
        case 6:
            multi_merge_unrolled<6>(out_first, out_last);
            break;
        case 7:
            multi_merge_unrolled<7>(out_first, out_last);
            break;
        case 8:
            multi_merge_unrolled<8>(out_first, out_last);
            break;
        case 9:
            multi_merge_unrolled<9>(out_first, out_last);
            break;
        case 10:
            multi_merge_unrolled<10>(out_first, out_last);
            break;
        default:
            multi_merge_k(out_first, out_last);
            break;
        }
    }
};

__STXXL_END_NAMESPACE

namespace std
{
    template <typename run_cursor_type,
              typename run_cursor_cmp_type>
    void swap(stxxl::loser_tree<run_cursor_type, run_cursor_cmp_type> & a,
              stxxl::loser_tree<run_cursor_type, run_cursor_cmp_type> & b)
    {
        a.swap(b);
    }
}

#endif // !STXXL_LOSERTREE_HEADER
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