andnotpostlist.h

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/* Copyright 2017 Olly Betts
 *
 * 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, see
 * <https://www.gnu.org/licenses/>.
 */
 
#ifndef XAPIAN_INCLUDED_ANDNOTPOSTLIST_H
#define XAPIAN_INCLUDED_ANDNOTPOSTLIST_H
 
#include "wrapperpostlist.h"
 
class PostListTree;
 
class AndNotPostList : public WrapperPostList {
    PostList* r;
 
    Xapian::docid r_did = 0;
 
  public:
    AndNotPostList(PostList* left, PostList* right, Xapian::doccount db_size)
        : WrapperPostList(left), r(right)
    {
        // We shortcut an empty shard and avoid creating a postlist tree for
        // it.
        Assert(db_size);
        // We calculate the estimate assuming independence.  With this
        // assumption, the estimate is the product of the estimates for the
        // sub-postlists (for the right side this is inverted by subtracting
        // from db_size), divided by db_size.
        double result = pl->get_termfreq();
        result = (result * (db_size - r->get_termfreq())) / db_size;
        termfreq = static_cast<Xapian::doccount>(result + 0.5);
    }
 
    ~AndNotPostList() { delete r; }
 
    PostList* next(double w_min);
 
    PostList* skip_to(Xapian::docid did, double w_min);
 
    PostList* check(Xapian::docid did, double w_min, bool& valid);
 
    std::string get_description() const;
};
 
#endif // XAPIAN_INCLUDED_ANDNOTPOSTLIST_H