xapian-core/api/terminfo.h

   1 /** @file terminfo.h
   2  * @brief Metadata for a term in a document
   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_TERMINFO_H
  22 #define XAPIAN_INCLUDED_TERMINFO_H
  23
  24 #include "api/smallvector.h"
  25 #include <xapian/types.h>
  26
  27 using namespace std;
  28
  29 /// Metadata for a term in a document
  30 class TermInfo {
  31     Xapian::termcount wdf;
  32
  33     /** Flag to indicate if this term was deleted from this document.
  34      *
  35      *  We flag entries as deleted instead of actually deleting them to avoid
  36      *  invalidating existing TermIterator objects.
  37      */
  38     bool deleted = false;
  39
  40     /** Positions at which the term occurs.
  41      *
  42      *  The entries are sorted in strictly increasing order (so duplicate
  43      *  entries are not allowed).
  44      */
  45     Xapian::VecCOW<Xapian::termpos> positions;
  46
  47   public:
  48     /** Constructor.
  49      *
  50      *  @param wdf_   Within-document frequency
  51      */
  52     explicit TermInfo(Xapian::termcount wdf_) : wdf(wdf_) {}
  53
  54     /** Constructor which also adds an initial position.
  55      *
  56      *  @param wdf_   Within-document frequency
  57      *  @param termpos  Position to add
  58      */
  59     TermInfo(Xapian::termcount wdf_, Xapian::termpos termpos) : wdf(wdf_) {
  60         positions.push_back(termpos);
  61     }
  62
  63     /// Get a pointer to the positions.
  64     const Xapian::VecCOW<Xapian::termpos>* get_positions() const {
  65         return &positions;
  66     }
  67
  68     /// Get the within-document frequency.
  69     Xapian::termcount get_wdf() const { return wdf; }
  70
  71     /** Increase within-document frequency.
  72      *
  73      *  @return true if the term was flagged as deleted before the operation.
  74      */
  75     bool increase_wdf(Xapian::termcount delta) {
  76         if (rare(deleted)) {
  77             deleted = false;
  78             wdf = delta;
  79             return true;
  80         }
  81         wdf += delta;
  82         return false;
  83     }
  84
  85     /// Decrease within-document frequency.
  86     void decrease_wdf(Xapian::termcount delta) {
  87         // Saturating arithmetic - don't let the wdf go below zero.
  88         if (wdf >= delta) {
  89             wdf -= delta;
  90         } else {
  91             wdf = 0;
  92         }
  93     }
  94
  95     bool remove() {
  96         if (deleted)
  97             return false;
  98         positions.clear();
  99         deleted = true;
 100         return true;
 101     }
 102
 103     /** Add a position.
 104      *
 105      *  If @a termpos is already present, this is a no-op.
 106      *
 107      *  @param wdf_inc  wdf increment
 108      *  @param termpos  Position to add
 109      *
 110      *  @return true if the term was flagged as deleted before the operation.
 111      */
 112     bool add_position(Xapian::termcount wdf_inc, Xapian::termpos termpos);
 113
 114     /** Append a position.
 115      *
 116      *  The position must be >= the largest currently in the list.
 117      */
 118     void append_position(Xapian::termpos termpos) {
 119         positions.push_back(termpos);
 120     }
 121
 122     /** Remove a position.
 123      *
 124      *  @param termpos  Position to remove
 125      *
 126      *  @return If @a termpos wasn't present, returns false.
 127      */
 128     bool remove_position(Xapian::termpos tpos);
 129
 130     /// Is this term flagged as deleted?
 131     bool is_deleted() const { return deleted; }
 132 };
 133
 134 #endif // XAPIAN_INCLUDED_TERMINFO_H