xapian-core/backends/glass/glass_positionlist.h

   1 /** @file glass_positionlist.h
   2  * @brief A position list in a glass database.
   3  */
   4 /* Copyright (C) 2005,2006,2008,2009,2010,2011,2013,2016,2017 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
  19  * USA
  20  */
  21
  22 #ifndef XAPIAN_HGUARD_GLASS_POSITIONLIST_H
  23 #define XAPIAN_HGUARD_GLASS_POSITIONLIST_H
  24
  25 #include <xapian/types.h>
  26
  27 #include "bitstream.h"
  28 #include "glass_cursor.h"
  29 #include "glass_lazytable.h"
  30 #include "pack.h"
  31 #include "backends/positionlist.h"
  32
  33 #include <string>
  34
  35 using namespace std;
  36
  37 class GlassPositionListTable : public GlassLazyTable {
  38   public:
  39     static string make_key(Xapian::docid did, const string & term) {
  40         string key;
  41         pack_string_preserving_sort(key, term);
  42         pack_uint_preserving_sort(key, did);
  43         return key;
  44     }
  45
  46     /** Create a new GlassPositionListTable object.
  47      *
  48      *  This method does not create or open the table on disk - you
  49      *  must call the create() or open() methods respectively!
  50      *
  51      *  @param dbdir            The directory the glass database is stored in.
  52      *  @param readonly         true if we're opening read-only, else false.
  53      */
  54     GlassPositionListTable(const string & dbdir, bool readonly)
  55         : GlassLazyTable("position", dbdir + "/position.", readonly) { }
  56
  57     GlassPositionListTable(int fd, off_t offset_, bool readonly_)
  58         : GlassLazyTable("position", fd, offset_, readonly_) { }
  59
  60     /** Pack a position list into a string.
  61      *
  62      *  @param s The string to append the position list data to.
  63      */
  64     void pack(string & s, const Xapian::VecCOW<Xapian::termpos> & vec) const;
  65
  66     /** Set the position list for term tname in document did.
  67      */
  68     void set_positionlist(Xapian::docid did, const string & tname,
  69                           const string & s) {
  70         add(make_key(did, tname), s);
  71     }
  72
  73     /// Delete the position list for term tname in document did.
  74     void delete_positionlist(Xapian::docid did, const string & tname) {
  75         del(make_key(did, tname));
  76     }
  77
  78     /// Return the number of entries in specified position list.
  79     Xapian::termcount positionlist_count(Xapian::docid did,
  80                                          const string & term) const;
  81 };
  82
  83 /** Base-class for a position list in a glass database. */
  84 class GlassBasePositionList : public PositionList {
  85     /// Copying is not allowed.
  86     GlassBasePositionList(const GlassBasePositionList&) = delete;
  87
  88     /// Assignment is not allowed.
  89     GlassBasePositionList& operator=(const GlassBasePositionList&) = delete;
  90
  91   protected:
  92     /// Interpolative decoder.
  93     BitReader rd;
  94
  95     /// Current entry.
  96     Xapian::termpos current_pos;
  97
  98     /// Last entry.
  99     Xapian::termpos last;
 100
 101     /// Number of entries.
 102     Xapian::termcount size;
 103
 104     /// Have we started iterating yet?
 105     bool have_started;
 106
 107   public:
 108     /// Default constructor.
 109     GlassBasePositionList() {}
 110
 111     /// Returns size of position list.
 112     Xapian::termcount get_approx_size() const;
 113
 114     /** Returns current position.
 115      *
 116      *  Either next() or skip_to() must have been called before this
 117      *  method can be called.
 118      */
 119     Xapian::termpos get_position() const;
 120
 121     /// Advance to the next term position in the list.
 122     bool next();
 123
 124     /// Advance to the first term position which is at least termpos.
 125     bool skip_to(Xapian::termpos termpos);
 126 };
 127
 128 /** A position list in a glass database. */
 129 class GlassPositionList : public GlassBasePositionList {
 130     /// The encoded positional data being read by rd.
 131     std::string pos_data;
 132
 133     /// Copying is not allowed.
 134     GlassPositionList(const GlassPositionList&) = delete;
 135
 136     /// Assignment is not allowed.
 137     GlassPositionList& operator=(const GlassPositionList&) = delete;
 138
 139   public:
 140     /// Construct and initialise with data.
 141     explicit
 142     GlassPositionList(const string& data);
 143
 144     /// Construct and initialise with data.
 145     GlassPositionList(const GlassTable* table,
 146                       Xapian::docid did,
 147                       const string& term);
 148 };
 149
 150 /** A reusable position list in a glass database. */
 151 class GlassRePositionList : public GlassBasePositionList {
 152     /// Cursor for locating multiple entries efficiently.
 153     GlassCursor cursor;
 154
 155     /// Copying is not allowed.
 156     GlassRePositionList(const GlassRePositionList&) = delete;
 157
 158     /// Assignment is not allowed.
 159     GlassRePositionList& operator=(const GlassRePositionList&) = delete;
 160
 161   public:
 162     /// Constructor.
 163     explicit
 164     GlassRePositionList(const GlassTable* table)
 165         : cursor(table) {}
 166
 167     /** Fill list with data, and move the position to the start. */
 168     void read_data(Xapian::docid did,
 169                    const string& term);
 170 };
 171
 172 #endif /* XAPIAN_HGUARD_GLASS_POSITIONLIST_H */