multiandpostlist.h

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/* Copyright (C) 2007,2009,2011,2017,2021 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
 */

#ifndef XAPIAN_INCLUDED_MULTIANDPOSTLIST_H
#define XAPIAN_INCLUDED_MULTIANDPOSTLIST_H

#include "multimatch.h"
#include "omassert.h"
#include "api/postlist.h"

#include <algorithm>

class MultiAndPostList : public PostList {
    struct ComparePostListTermFreqAscending {
        bool operator()(const PostList *a, const PostList *b) const {
            return a->get_termfreq_est() < b->get_termfreq_est();
        }
    };

    void operator=(const MultiAndPostList &);

    MultiAndPostList(const MultiAndPostList &);

    Xapian::docid did;

    size_t n_kids;

    PostList ** plist;

    double * max_wt;

    double max_total;

    Xapian::doccount db_size;

    MultiMatch *matcher;

    double new_min(double w_min, size_t n) {
        return w_min - (max_total - max_wt[n]);
    }

    void next_helper(size_t n, double w_min) {
        PostList * res = plist[n]->next(new_min(w_min, n));
        if (res) {
            delete plist[n];
            plist[n] = res;
            if (max_wt[n] > 0)
                matcher->recalc_maxweight();
        }
    }

    void skip_to_helper(size_t n, Xapian::docid did_min, double w_min) {
        PostList * res = plist[n]->skip_to(did_min, new_min(w_min, n));
        if (res) {
            delete plist[n];
            plist[n] = res;
            if (max_wt[n] > 0)
                matcher->recalc_maxweight();
        }
    }

    void check_helper(size_t n, Xapian::docid did_min, double w_min,
                      bool &valid) {
        PostList * res = plist[n]->check(did_min, new_min(w_min, n), valid);
        if (res) {
            delete plist[n];
            plist[n] = res;
            if (max_wt[n] > 0)
                matcher->recalc_maxweight();
        }
    }

    void allocate_plist_and_max_wt();

    PostList * find_next_match(double w_min);

  public:
    template<class RandomItor>
    MultiAndPostList(RandomItor pl_begin, RandomItor pl_end,
                     MultiMatch * matcher_, Xapian::doccount db_size_)
        : did(0), n_kids(pl_end - pl_begin), plist(NULL), max_wt(NULL),
          max_total(0), db_size(db_size_), matcher(matcher_)
    {
        allocate_plist_and_max_wt();

        // Copy the postlists in ascending termfreq order, since it will
        // be more efficient to look at the shorter lists first, and skip
        // the longer lists based on those.
        std::partial_sort_copy(pl_begin, pl_end, plist, plist + n_kids,
                               ComparePostListTermFreqAscending());
    }

    MultiAndPostList(PostList *l, PostList *r,
                     double lmax, double rmax,
                     MultiMatch * matcher_, Xapian::doccount db_size_)
        : did(0), n_kids(2), plist(NULL), max_wt(NULL),
          max_total(lmax + rmax), db_size(db_size_), matcher(matcher_)
    {
        // Even if we're the decay product of an OrPostList, we may want to
        // swap here, as the subqueries may also have decayed and so their
        // estimated termfreqs may have changed.
        if (l->get_termfreq_est() < r->get_termfreq_est()) {
            std::swap(l, r);
            std::swap(lmax, rmax);
        }
        allocate_plist_and_max_wt();
        // Put the least frequent postlist first.
        plist[0] = r;
        plist[1] = l;
        max_wt[0] = rmax;
        max_wt[1] = lmax;
    }

    ~MultiAndPostList();

    Xapian::doccount get_termfreq_min() const;

    Xapian::doccount get_termfreq_max() const;

    Xapian::doccount get_termfreq_est() const;

    TermFreqs get_termfreq_est_using_stats(
        const Xapian::Weight::Internal & stats) const;

    double get_maxweight() const;

    Xapian::docid get_docid() const;

    Xapian::termcount get_doclength() const;

    Xapian::termcount get_unique_terms() const;

    double get_weight() const;

    bool at_end() const;

    double recalc_maxweight();

    PostList* next(double w_min);

    PostList* skip_to(Xapian::docid, double w_min);

    std::string get_description() const;

    Xapian::termcount get_wdf() const;

    Xapian::termcount count_matching_subqs() const;

    void gather_position_lists(OrPositionList* orposlist);
};

#endif // XAPIAN_INCLUDED_MULTIANDPOSTLIST_H