matcher/multiandpostlist.cc

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/* Copyright (C) 2007,2009,2012 Olly Betts
 * Copyright (C) 2009 Lemur Consulting Ltd
 *
 * This program 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 2 of the
 * License, or (at your option) any later version.
 *
 * This program 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include <config.h>

#include "multiandpostlist.h"
#include "omassert.h"
#include "debuglog.h"

void
MultiAndPostList::allocate_plist_and_max_wt()
{
    plist = new PostList * [n_kids];
    try {
        max_wt = new Xapian::weight [n_kids];
    } catch (...) {
        delete [] plist;
        plist = NULL;
        throw;
    }
}

MultiAndPostList::~MultiAndPostList()
{
    if (plist) {
        for (size_t i = 0; i < n_kids; ++i) {
            delete plist[i];
        }
        delete [] plist;
    }
    delete [] max_wt;
}

Xapian::doccount
MultiAndPostList::get_termfreq_min() const
{
    // The number of matching documents is minimised when we have the minimum
    // number of matching documents from each sub-postlist, and these are
    // maximally disjoint.
    Xapian::doccount sum = plist[0]->get_termfreq_min();
    if (sum) {
        for (size_t i = 1; i < n_kids; ++i) {
            Xapian::doccount sum_old = sum;
            sum += plist[i]->get_termfreq_min();
            // If sum < sum_old, the calculation overflowed and the true sum
            // must be > db_size.  Since we added a value <= db_size,
            // subtracting db_size must un-overflow us.
            if (sum >= sum_old && sum <= db_size) {
                // It's possible there's no overlap.
                return 0;
            }
            sum -= db_size;
        }
        AssertRelParanoid(sum,<=,MultiAndPostList::get_termfreq_est());
    }
    return sum;
}

Xapian::doccount
MultiAndPostList::get_termfreq_max() const
{
    // We can't match more documents than the least of our sub-postlists.
    Xapian::doccount result = plist[0]->get_termfreq_max();
    for (size_t i = 1; i < n_kids; ++i) {
        Xapian::doccount tf = plist[i]->get_termfreq_max();
        if (tf < result) result = tf;
    }
    return result;
}

Xapian::doccount
MultiAndPostList::get_termfreq_est() const
{
    if (rare(db_size == 0))
        RETURN(0);
    // We calculate the estimate assuming independence.  With this assumption,
    // the estimate is the product of the estimates for the sub-postlists
    // divided by db_size (n_kids - 1) times.
    double result(plist[0]->get_termfreq_est());
    for (size_t i = 1; i < n_kids; ++i) {
        result = (result * plist[i]->get_termfreq_est()) / db_size;
    }
    return static_cast<Xapian::doccount>(result + 0.5);
}

TermFreqs
MultiAndPostList::get_termfreq_est_using_stats(
        const Xapian::Weight::Internal & stats) const 
{
    LOGCALL(MATCH, TermFreqs, "MultiAndPostList::get_termfreq_est_using_stats", stats);
    // We calculate the estimate assuming independence.  With this assumption,
    // the estimate is the product of the estimates for the sub-postlists
    // divided by db_size (n_kids - 1) times.
    TermFreqs freqs(plist[0]->get_termfreq_est_using_stats(stats));

    double freqest = double(freqs.termfreq);
    double relfreqest = double(freqs.reltermfreq);

    // Our caller should have ensured this.
    Assert(stats.collection_size);

    for (size_t i = 1; i < n_kids; ++i) {
        freqs = plist[i]->get_termfreq_est_using_stats(stats);

        // If the collection is empty, freqest should be 0 already, so leave
        // it alone.
        freqest = (freqest * freqs.termfreq) / stats.collection_size;

        // If the rset is empty, relfreqest should be 0 already, so leave
        // it alone.
        if (stats.rset_size != 0)
            relfreqest = (relfreqest * freqs.reltermfreq) / stats.rset_size;
    }

    RETURN(TermFreqs(static_cast<Xapian::doccount>(freqest + 0.5),
                     static_cast<Xapian::doccount>(relfreqest + 0.5)));
}

Xapian::weight
MultiAndPostList::get_maxweight() const
{
    return max_total;
}

Xapian::docid
MultiAndPostList::get_docid() const
{
    return did;
}

Xapian::termcount
MultiAndPostList::get_doclength() const
{
    Assert(did);
    Xapian::termcount doclength = plist[0]->get_doclength();
    for (size_t i = 1; i < n_kids; ++i) {
        AssertEq(doclength, plist[i]->get_doclength());
    }
    return doclength;
}

Xapian::weight
MultiAndPostList::get_weight() const
{
    Assert(did);
    Xapian::weight result = 0;
    for (size_t i = 0; i < n_kids; ++i) {
        result += plist[i]->get_weight();
    }
    return result;
}

bool
MultiAndPostList::at_end() const
{
    return (did == 0);
}

Xapian::weight
MultiAndPostList::recalc_maxweight()
{
    max_total = 0.0;
    for (size_t i = 0; i < n_kids; ++i) {
        Xapian::weight new_max = plist[i]->recalc_maxweight();
        max_wt[i] = new_max;
        max_total += new_max;
    }
    return max_total;
}

PostList *
MultiAndPostList::find_next_match(Xapian::weight w_min)
{
advanced_plist0:
    if (plist[0]->at_end()) {
        did = 0;
        return NULL;
    }
    did = plist[0]->get_docid();
    for (size_t i = 1; i < n_kids; ++i) {
        bool valid;
        check_helper(i, did, w_min, valid);
        if (!valid) {
            next_helper(0, w_min);
            goto advanced_plist0;
        }
        if (plist[i]->at_end()) {
            did = 0;
            return NULL;
        }
        Xapian::docid new_did = plist[i]->get_docid();
        if (new_did != did) {
            skip_to_helper(0, new_did, w_min);
            goto advanced_plist0;
        }
    }
    return NULL;
}

PostList *
MultiAndPostList::next(Xapian::weight w_min)
{
    next_helper(0, w_min);
    return find_next_match(w_min);
}

PostList *
MultiAndPostList::skip_to(Xapian::docid did_min, Xapian::weight w_min)
{
    skip_to_helper(0, did_min, w_min);
    return find_next_match(w_min);
}

std::string
MultiAndPostList::get_description() const
{
    string desc("(");
    desc += plist[0]->get_description();
    for (size_t i = 1; i < n_kids; ++i) {
        desc += " AND ";
        desc += plist[i]->get_description();
    }
    desc += ')';
    return desc;
}

Xapian::termcount
MultiAndPostList::get_wdf() const
{
    Xapian::termcount totwdf = 0;
    for (size_t i = 0; i < n_kids; ++i) {
        totwdf += plist[i]->get_wdf();
    }
    return totwdf;
}

Xapian::termcount
MultiAndPostList::count_matching_subqs() const
{
    Xapian::termcount total = 0;
    for (size_t i = 0; i < n_kids; ++i) {
        total += plist[i]->count_matching_subqs();
    }
    return total;
}

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