stream/test_sorted_runs.cpp

This is an example of how to use some basic algorithms from stream package. This example shows how to create sorted_runs data structure from sorted sequences using stream::from_sorted_sequences specialization of stream::runs_creator class

/***************************************************************************
 *  stream/test_sorted_runs.cpp
 *
 *  Part of the STXXL. See http://stxxl.sourceforge.net
 *
 *  Copyright (C) 2003 Roman Dementiev <dementiev@mpi-sb.mpg.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)
 **************************************************************************/


#include <stxxl/stream>


typedef unsigned value_type;

struct Cmp : public std::binary_function<value_type, value_type, bool>
{
    typedef unsigned value_type;
    bool operator () (const value_type & a, const value_type & b) const
    {
        return a < b;
    }
    value_type min_value()
    {
        return (std::numeric_limits<value_type>::min)();
    }
    value_type max_value()
    {
        return (std::numeric_limits<value_type>::max)();
    }
};


int main()
{
    // special parameter type
    typedef stxxl::stream::from_sorted_sequences<value_type> InputType;
    typedef stxxl::stream::runs_creator<InputType, Cmp, 4096, stxxl::RC> CreateRunsAlg;
    typedef CreateRunsAlg::sorted_runs_type SortedRunsType;

    unsigned size = 30 * 1024 * 128 / (sizeof(value_type) * 2);

    unsigned i = 0;

    Cmp c;
    CreateRunsAlg SortedRuns(c, 1024 * 128);
    value_type oldcrc(0);

    stxxl::random_number32 rnd;
    stxxl::random_number<> rnd_max;
    unsigned cnt = size;
    while (cnt > 0)
    {
        unsigned run_size = rnd_max(cnt) + 1;           // random run length
        cnt -= run_size;
        STXXL_MSG("current run size:" << run_size);

        std::vector<unsigned> tmp(run_size);            // create temp storage for current run
        std::generate(tmp.begin(), tmp.end(), rnd);     // fill with random numbers
        std::sort(tmp.begin(), tmp.end(), c);           // sort
        for (unsigned j = 0; j < run_size; ++j)
        {
            oldcrc += tmp[j];
            SortedRuns.push(tmp[j]);                    // push sorted values to the current run
        }
        SortedRuns.finish();                            // finish current run
    }


    SortedRunsType Runs = SortedRuns.result();          // get sorted_runs data structure
    assert(check_sorted_runs(Runs, Cmp()));
    // merge the runs
    stxxl::stream::runs_merger<SortedRunsType, Cmp> merger(Runs, Cmp(), 1024 * 128 / 10 * stxxl::sort_memory_usage_factor());
    stxxl::vector<value_type> array;
    STXXL_MSG(size << " " << Runs.elements);
    STXXL_MSG("CRC: " << oldcrc);
    value_type crc(0);
    for (i = 0; i < size; ++i)
    {
        crc += *merger;
        array.push_back(*merger);
        ++merger;
    }
    STXXL_MSG("CRC: " << crc);
    assert(stxxl::is_sorted(array.begin(), array.end(), Cmp()));
    assert(merger.empty());

    return 0;
}

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