xapian-core/api/decvalwtsource.cc

   1 /** @file decvalwtsource.cc
   2  * @brief A posting source which returns decreasing weights from a value.
   3  */
   4 /* Copyright (C) 2009 Lemur Consulting Ltd
   5  * Copyright (C) 2011,2012,2015,2016 Olly Betts
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  20  */
  21
  22 #include <config.h>
  23
  24 #include "xapian/postingsource.h"
  25 #include "xapian/error.h"
  26 #include "net/length.h"
  27 #include "serialise-double.h"
  28 #include <cmath>
  29
  30 using namespace Xapian;
  31
  32 DecreasingValueWeightPostingSource::DecreasingValueWeightPostingSource(
  33     Xapian::valueno slot_,
  34     Xapian::docid range_start_,
  35     Xapian::docid range_end_)
  36         : Xapian::ValueWeightPostingSource(slot_),
  37           range_start(range_start_),
  38           range_end(range_end_)
  39 {
  40 }
  41
  42 double
  43 DecreasingValueWeightPostingSource::get_weight() const {
  44     return curr_weight;
  45 }
  46
  47 Xapian::DecreasingValueWeightPostingSource *
  48 DecreasingValueWeightPostingSource::clone() const {
  49     return new DecreasingValueWeightPostingSource(get_slot(), range_start,
  50                                                   range_end);
  51 }
  52
  53 std::string
  54 DecreasingValueWeightPostingSource::name() const {
  55     return "Xapian::DecreasingValueWeightPostingSource";
  56 }
  57
  58 std::string
  59 DecreasingValueWeightPostingSource::serialise() const {
  60     std::string result;
  61     result += encode_length(get_slot());
  62     result += encode_length(range_start);
  63     result += encode_length(range_end);
  64     return result;
  65 }
  66
  67 Xapian::DecreasingValueWeightPostingSource *
  68 DecreasingValueWeightPostingSource::unserialise(const std::string &s) const {
  69     const char * pos = s.data();
  70     const char * end = pos + s.size();
  71     Xapian::valueno new_slot;
  72     Xapian::docid new_range_start, new_range_end;
  73     decode_length(&pos, end, new_slot);
  74     decode_length(&pos, end, new_range_start);
  75     decode_length(&pos, end, new_range_end);
  76     if (pos != end)
  77         throw Xapian::NetworkError("Junk at end of serialised "
  78                                    "DecreasingValueWeightPostingSource");
  79     return new DecreasingValueWeightPostingSource(new_slot, new_range_start,
  80                                                   new_range_end);
  81 }
  82
  83 void
  84 DecreasingValueWeightPostingSource::init(const Xapian::Database & db_) {
  85     Xapian::ValueWeightPostingSource::init(db_);
  86     if (range_end == 0 || get_database().get_doccount() <= range_end)
  87         items_at_end = false;
  88     else
  89         items_at_end = true;
  90 }
  91
  92 void
  93 DecreasingValueWeightPostingSource::skip_if_in_range(double min_wt)
  94 {
  95     if (ValueWeightPostingSource::at_end()) return;
  96     curr_weight = Xapian::ValueWeightPostingSource::get_weight();
  97     Xapian::docid docid = Xapian::ValueWeightPostingSource::get_docid();
  98     if (docid >= range_start && (range_end == 0 || docid <= range_end)) {
  99         if (items_at_end) {
 100             if (curr_weight < min_wt) {
 101                 // skip to end of range.
 102                 ValueWeightPostingSource::skip_to(range_end + 1, min_wt);
 103                 if (!ValueWeightPostingSource::at_end())
 104                     curr_weight = Xapian::ValueWeightPostingSource::get_weight();
 105             }
 106         } else {
 107             if (curr_weight < min_wt) {
 108                 // terminate early.
 109                 done();
 110             } else {
 111                 // Update max_weight.
 112                 set_maxweight(curr_weight);
 113             }
 114         }
 115     }
 116 }
 117
 118 void
 119 DecreasingValueWeightPostingSource::next(double min_wt) {
 120     if (get_maxweight() < min_wt) {
 121         done();
 122         return;
 123     }
 124     Xapian::ValueWeightPostingSource::next(min_wt);
 125     skip_if_in_range(min_wt);
 126 }
 127
 128 void
 129 DecreasingValueWeightPostingSource::skip_to(Xapian::docid min_docid,
 130                                             double min_wt) {
 131     if (get_maxweight() < min_wt) {
 132         done();
 133         return;
 134     }
 135     Xapian::ValueWeightPostingSource::skip_to(min_docid, min_wt);
 136     skip_if_in_range(min_wt);
 137 }
 138
 139 bool
 140 DecreasingValueWeightPostingSource::check(Xapian::docid min_docid,
 141                                           double min_wt) {
 142     if (get_maxweight() < min_wt) {
 143         done();
 144         return true;
 145     }
 146     bool valid = Xapian::ValueWeightPostingSource::check(min_docid, min_wt);
 147     if (valid) {
 148         skip_if_in_range(min_wt);
 149     }
 150     return valid;
 151 }
 152
 153 std::string
 154 DecreasingValueWeightPostingSource::get_description() const {
 155     return "DecreasingValueWeightPostingSource()";
 156 }