beagled/Lucene.Net/Search/TermScorer.cs

   1 /*
   2  * Copyright 2004 The Apache Software Foundation
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  * http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 using System;
  17 using TermDocs = Lucene.Net.Index.TermDocs;
  18 namespace Lucene.Net.Search
  19 {
  20
  21         sealed class TermScorer:Scorer
  22         {
  23                 private Weight weight;
  24                 private TermDocs termDocs;
  25                 private byte[] norms;
  26                 private float weightValue;
  27                 private int doc;
  28
  29                 private int[] docs = new int[32]; // buffered doc numbers
  30                 private int[] freqs = new int[32]; // buffered term freqs
  31                 private int pointer;
  32                 private int pointerMax;
  33
  34                 private const int SCORE_CACHE_SIZE = 32;
  35                 private float[] scoreCache = new float[SCORE_CACHE_SIZE];
  36
  37                 internal TermScorer(Weight weight, TermDocs td, Similarity similarity, byte[] norms) : base(similarity)
  38                 {
  39                         this.weight = weight;
  40                         this.termDocs = td;
  41                         this.norms = norms;
  42                         this.weightValue = weight.Value;
  43
  44                         for (int i = 0; i < SCORE_CACHE_SIZE; i++)
  45                                 scoreCache[i] = GetSimilarity().Tf(i) * weightValue;
  46                 }
  47
  48                 public override int Doc()
  49                 {
  50                         return doc;
  51                 }
  52
  53                 public override bool Next()
  54                 {
  55                         pointer++;
  56                         if (pointer >= pointerMax)
  57                         {
  58                                 pointerMax = termDocs.Read(docs, freqs); // refill buffer
  59                                 if (pointerMax != 0)
  60                                 {
  61                                         pointer = 0;
  62                                 }
  63                                 else
  64                                 {
  65                                         termDocs.Close(); // close stream
  66                                         doc = System.Int32.MaxValue; // set to sentinel value
  67                                         return false;
  68                                 }
  69                         }
  70                         doc = docs[pointer];
  71                         return true;
  72                 }
  73
  74                 public override float Score()
  75                 {
  76                         int f = freqs[pointer];
  77                         float raw = f < SCORE_CACHE_SIZE ? scoreCache[f] : GetSimilarity().Tf(f) * weightValue; // cache miss
  78
  79                         return raw * Similarity.DecodeNorm(norms[doc]); // normalize for Field
  80                 }
  81
  82                 public override bool SkipTo(int target)
  83                 {
  84                         // first scan in cache
  85                         for (pointer++; pointer < pointerMax; pointer++)
  86                         {
  87                                 if (docs[pointer] >= target)
  88                                 {
  89                                         doc = docs[pointer];
  90                                         return true;
  91                                 }
  92                         }
  93
  94                         // not found in cache, seek underlying stream
  95                         bool result = termDocs.SkipTo(target);
  96                         if (result)
  97                         {
  98                                 pointerMax = 1;
  99                                 pointer = 0;
 100                                 docs[pointer] = doc = termDocs.Doc();
 101                                 freqs[pointer] = termDocs.Freq();
 102                         }
 103                         else
 104                         {
 105                                 doc = System.Int32.MaxValue;
 106                         }
 107                         return result;
 108                 }
 109
 110                 public override Explanation Explain(int doc)
 111                 {
 112                         TermQuery query = (TermQuery) weight.Query;
 113                         Explanation tfExplanation = new Explanation();
 114                         int tf = 0;
 115                         while (pointer < pointerMax)
 116                         {
 117                                 if (docs[pointer] == doc)
 118                                         tf = freqs[pointer];
 119                                 pointer++;
 120                         }
 121                         if (tf == 0)
 122                         {
 123                                 while (termDocs.Next())
 124                                 {
 125                                         if (termDocs.Doc() == doc)
 126                                         {
 127                                                 tf = termDocs.Freq();
 128                                         }
 129                                 }
 130                         }
 131                         termDocs.Close();
 132                         tfExplanation.SetValue(GetSimilarity().Tf(tf));
 133                         tfExplanation.SetDescription("tf(termFreq(" + query.GetTerm() + ")=" + tf + ")");
 134
 135                         return tfExplanation;
 136                 }
 137
 138                 public override System.String ToString()
 139                 {
 140                         return "scorer(" + weight + ")";
 141                 }
 142         }
 143 }