xapian-core/api/vectortermlist.h

   1 /** @file
   2  * @brief A vector-like container of terms which can be iterated.
   3  */
   4 /* Copyright (C) 2011,2012,2017 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_VECTORTERMLIST_H
  22 #define XAPIAN_INCLUDED_VECTORTERMLIST_H
  23
  24 #include "xapian/types.h"
  25
  26 #include "net/length.h"
  27 #include "termlist.h"
  28
  29 /** This class stores a list of terms.
  30  *
  31  *  To be memory efficient, we store the terms in a single string using a
  32  *  suitable simple encoding.  This way the number of bytes needed will
  33  *  usually be the sum of the lengths of all the terms plus the number of
  34  *  terms.  If we used std::vector<std::string> here like we used to, that
  35  *  would need something like an additional 30 bytes per term (30 calculated
  36  *  for GCC 4.x on x86_64).
  37  */
  38 class VectorTermList : public TermList {
  39     /// The encoded terms.
  40     std::string data;
  41
  42     /// Pointer to the next term's data, or NULL if we are at end.
  43     const char * p;
  44
  45     /// The number of terms in the list.
  46     Xapian::termcount num_terms;
  47
  48     /// The current term.
  49     std::string current_term;
  50
  51   public:
  52     template<typename I>
  53     VectorTermList(I begin, I end) : num_terms(0)
  54     {
  55         // First calculate how much space we'll need so we can reserve it.
  56         size_t total_size = 0;
  57         for (I i = begin; i != end; ++i) {
  58             ++num_terms;
  59             const std::string & s = *i;
  60             total_size += s.size() + 1;
  61             if (s.size() >= 255) {
  62                 // Not a common case, so just assume the worst case rather than
  63                 // trying to carefully calculate the exact size.
  64                 total_size += 5;
  65             }
  66         }
  67         data.reserve(total_size);
  68
  69         // Now encode all the terms into data.
  70         for (I i = begin; i != end; ++i) {
  71             const std::string & s = *i;
  72             data += encode_length(s.size());
  73             data += s;
  74         }
  75
  76         p = data.data();
  77     }
  78
  79     Xapian::termcount get_approx_size() const;
  80
  81     std::string get_termname() const;
  82
  83     Xapian::termcount get_wdf() const;
  84
  85     Xapian::doccount get_termfreq() const;
  86
  87     TermList * next();
  88
  89     TermList * skip_to(const std::string &);
  90
  91     bool at_end() const;
  92
  93     Xapian::termcount positionlist_count() const;
  94
  95     Xapian::PositionIterator positionlist_begin() const;
  96 };
  97
  98 #endif // XAPIAN_INCLUDED_VECTORTERMLIST_H