xapian-core/matcher/andnotpostlist.h

   1 /** @file
   2  * @brief PostList class implementing Query::OP_AND_NOT
   3  */
   4 /* Copyright 2017 Olly Betts
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License as
   8  * published by the Free Software Foundation; either version 2 of the
   9  * License, or (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  19  */
  20
  21 #ifndef XAPIAN_INCLUDED_ANDNOTPOSTLIST_H
  22 #define XAPIAN_INCLUDED_ANDNOTPOSTLIST_H
  23
  24 #include "wrapperpostlist.h"
  25
  26 class PostListTree;
  27
  28 /// PostList class implementing Query::OP_AND_NOT
  29 class AndNotPostList : public WrapperPostList {
  30     /// Right-hand side of OP_NOT.
  31     PostList* r;
  32
  33     /// Current docid from r (or 0).
  34     Xapian::docid r_did = 0;
  35
  36   public:
  37     AndNotPostList(PostList* left, PostList* right, Xapian::doccount db_size)
  38         : WrapperPostList(left), r(right)
  39     {
  40         // We shortcut an empty shard and avoid creating a postlist tree for
  41         // it.
  42         Assert(db_size);
  43         // We calculate the estimate assuming independence.  With this
  44         // assumption, the estimate is the product of the estimates for the
  45         // sub-postlists (for the right side this is inverted by subtracting
  46         // from db_size), divided by db_size.
  47         double result = pl->get_termfreq();
  48         result = (result * (db_size - r->get_termfreq())) / db_size;
  49         termfreq = static_cast<Xapian::doccount>(result + 0.5);
  50     }
  51
  52     ~AndNotPostList() { delete r; }
  53
  54     PostList* next(double w_min);
  55
  56     PostList* skip_to(Xapian::docid did, double w_min);
  57
  58     PostList* check(Xapian::docid did, double w_min, bool& valid);
  59
  60     std::string get_description() const;
  61 };
  62
  63 #endif // XAPIAN_INCLUDED_ANDNOTPOSTLIST_H