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From da...@apache.org
Subject [05/50] [abbrv] lucene-solr:jira/solr-11702: LUCENE-8116: SimScorer now only takes a frequency and a norm as per-document scoring factors.
Date Thu, 11 Jan 2018 08:00:41 GMT
LUCENE-8116: SimScorer now only takes a frequency and a norm as per-document scoring factors.


Project: http://git-wip-us.apache.org/repos/asf/lucene-solr/repo
Commit: http://git-wip-us.apache.org/repos/asf/lucene-solr/commit/8fd7ead9
Tree: http://git-wip-us.apache.org/repos/asf/lucene-solr/tree/8fd7ead9
Diff: http://git-wip-us.apache.org/repos/asf/lucene-solr/diff/8fd7ead9

Branch: refs/heads/jira/solr-11702
Commit: 8fd7ead940f69a892dfc951a1aa042e8cae806c1
Parents: 8836fda
Author: Adrien Grand <jpountz@gmail.com>
Authored: Thu Jan 4 15:13:36 2018 +0100
Committer: Adrien Grand <jpountz@gmail.com>
Committed: Thu Jan 4 15:13:36 2018 +0100

----------------------------------------------------------------------
 lucene/CHANGES.txt                              |   6 +
 .../classification/KNearestFuzzyClassifier.java |   2 +-
 .../KNearestNeighborClassifier.java             |   2 +-
 .../org/apache/lucene/search/BooleanWeight.java |   2 +-
 .../apache/lucene/search/ExactPhraseScorer.java |   7 +-
 .../org/apache/lucene/search/IndexSearcher.java |  45 +----
 .../org/apache/lucene/search/LeafSimScorer.java |  74 +++++++
 .../apache/lucene/search/MultiPhraseQuery.java  |  29 +--
 .../org/apache/lucene/search/PhraseQuery.java   |  13 +-
 .../lucene/search/SloppyPhraseScorer.java       |   7 +-
 .../org/apache/lucene/search/SynonymQuery.java  |  35 ++--
 .../org/apache/lucene/search/TermQuery.java     |  15 +-
 .../org/apache/lucene/search/TermScorer.java    |  11 +-
 .../org/apache/lucene/search/package-info.java  |   4 +-
 .../lucene/search/similarities/Axiomatic.java   |  10 +-
 .../search/similarities/BM25Similarity.java     | 142 +++++---------
 .../lucene/search/similarities/BasicStats.java  |   2 +-
 .../search/similarities/BooleanSimilarity.java  |  51 ++---
 .../search/similarities/DFISimilarity.java      |   6 +-
 .../search/similarities/DFRSimilarity.java      |   8 +-
 .../search/similarities/IBSimilarity.java       |   8 +-
 .../similarities/LMDirichletSimilarity.java     |  10 +-
 .../similarities/LMJelinekMercerSimilarity.java |  10 +-
 .../search/similarities/LMSimilarity.java       |   2 +-
 .../search/similarities/MultiSimilarity.java    |  37 +---
 .../similarities/PerFieldSimilarityWrapper.java |  22 +--
 .../lucene/search/similarities/Similarity.java  |  99 ++++------
 .../search/similarities/SimilarityBase.java     |  79 +++-----
 .../search/similarities/TFIDFSimilarity.java    | 133 +++++--------
 .../apache/lucene/search/spans/SpanScorer.java  |   6 +-
 .../apache/lucene/search/spans/SpanWeight.java  |  22 +--
 .../apache/lucene/search/spans/TermSpans.java   |   4 +-
 .../apache/lucene/index/TestCustomNorms.java    |   7 +-
 .../apache/lucene/index/TestCustomTermFreq.java |   9 +-
 .../lucene/index/TestFieldInvertState.java      |   8 +-
 .../apache/lucene/index/TestIndexSorting.java   |   9 +-
 .../lucene/index/TestMaxTermFrequency.java      |  12 +-
 .../test/org/apache/lucene/index/TestNorms.java |   7 +-
 .../lucene/index/TestUniqueTermCount.java       |   8 +-
 .../apache/lucene/search/JustCompileSearch.java |   7 +-
 .../org/apache/lucene/search/TestBoolean2.java  |   4 +-
 .../search/TestBooleanQueryVisitSubscorers.java |  12 +-
 .../lucene/search/TestBooleanRewrites.java      |   2 +-
 .../apache/lucene/search/TestConjunctions.java  |  12 +-
 .../lucene/search/TestDocValuesScoring.java     | 192 -------------------
 .../lucene/search/TestMinShouldMatch2.java      |   9 +-
 .../lucene/search/TestSimilarityProvider.java   |  23 +--
 .../lucene/search/TestSubScorerFreqs.java       |  12 +-
 .../similarities/TestClassicSimilarity.java     |   3 +-
 .../search/similarities/TestSimilarityBase.java |  11 +-
 .../search/spans/TestFieldMaskingSpanQuery.java |   4 +-
 .../lucene/index/memory/TestMemoryIndex.java    |   8 +-
 .../search/TestDiversifiedTopDocsCollector.java | 132 ++++++++-----
 .../function/valuesource/IDFValueSource.java    |   2 +-
 .../function/valuesource/NormValueSource.java   |  10 +-
 .../function/valuesource/TFValueSource.java     |   2 +-
 .../queries/payloads/PayloadScoreQuery.java     |   7 +-
 .../queries/payloads/SpanPayloadCheckQuery.java |   4 +-
 .../function/TestLongNormValueSource.java       |   2 +-
 .../queries/function/TestValueSources.java      |   8 +-
 .../lucene/search/TermAutomatonQuery.java       |   8 +-
 .../lucene/search/TermAutomatonScorer.java      |   7 +-
 .../lucene/index/BaseNormsFormatTestCase.java   |   7 +-
 .../org/apache/lucene/search/QueryUtils.java    |  10 +-
 .../similarities/AssertingSimilarity.java       |  95 ++++-----
 .../similarities/BaseSimilarityTestCase.java    | 140 ++------------
 .../search/spans/AssertingSpanWeight.java       |   4 +-
 .../similarities/BaseSimilarityTestCase.java    |   2 +-
 68 files changed, 606 insertions(+), 1096 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/CHANGES.txt
----------------------------------------------------------------------
diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index ff94809..16050d1 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -32,6 +32,9 @@ API Changes
 * LUCENE-8012: Explanation now takes Number rather than float (Alan Woodward, 
   Robert Muir)
 
+* LUCENE-8116: SimScorer now only takes a frequency and a norm as per-document
+  scoring factors. (Adrien Grand)
+
 Changes in Runtime Behavior
 
 * LUCENE-7837: Indices that were created before the previous major version
@@ -46,6 +49,9 @@ Changes in Runtime Behavior
 * LUCENE-7996: FunctionQuery and FunctionScoreQuery now return a score of 0
   when the function produces a negative value. (Adrien Grand)
 
+* LUCENE-8116: Similarities now score fields that omit norms as if the norm was
+  1. This might change score values on fields that omit norms. (Adrien Grand)
+
 Improvements
 
 * LUCENE-7997: Add BaseSimilarityTestCase to sanity check similarities.

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/classification/src/java/org/apache/lucene/classification/KNearestFuzzyClassifier.java
----------------------------------------------------------------------
diff --git a/lucene/classification/src/java/org/apache/lucene/classification/KNearestFuzzyClassifier.java b/lucene/classification/src/java/org/apache/lucene/classification/KNearestFuzzyClassifier.java
index cbd241b..14f9a27 100644
--- a/lucene/classification/src/java/org/apache/lucene/classification/KNearestFuzzyClassifier.java
+++ b/lucene/classification/src/java/org/apache/lucene/classification/KNearestFuzzyClassifier.java
@@ -213,7 +213,7 @@ public class KNearestFuzzyClassifier implements Classifier<BytesRef> {
         ", classFieldName='" + classFieldName + '\'' +
         ", k=" + k +
         ", query=" + query +
-        ", similarity=" + indexSearcher.getSimilarity(true) +
+        ", similarity=" + indexSearcher.getSimilarity() +
         '}';
   }
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/classification/src/java/org/apache/lucene/classification/KNearestNeighborClassifier.java
----------------------------------------------------------------------
diff --git a/lucene/classification/src/java/org/apache/lucene/classification/KNearestNeighborClassifier.java b/lucene/classification/src/java/org/apache/lucene/classification/KNearestNeighborClassifier.java
index f0391f4..e6ad4a3 100644
--- a/lucene/classification/src/java/org/apache/lucene/classification/KNearestNeighborClassifier.java
+++ b/lucene/classification/src/java/org/apache/lucene/classification/KNearestNeighborClassifier.java
@@ -251,7 +251,7 @@ public class KNearestNeighborClassifier implements Classifier<BytesRef> {
         ", classFieldName='" + classFieldName + '\'' +
         ", k=" + k +
         ", query=" + query +
-        ", similarity=" + indexSearcher.getSimilarity(true) +
+        ", similarity=" + indexSearcher.getSimilarity() +
         '}';
   }
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/BooleanWeight.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/BooleanWeight.java b/lucene/core/src/java/org/apache/lucene/search/BooleanWeight.java
index 900a77f..fffdd09 100644
--- a/lucene/core/src/java/org/apache/lucene/search/BooleanWeight.java
+++ b/lucene/core/src/java/org/apache/lucene/search/BooleanWeight.java
@@ -48,7 +48,7 @@ final class BooleanWeight extends Weight {
     super(query);
     this.query = query;
     this.scoreMode = scoreMode;
-    this.similarity = searcher.getSimilarity(scoreMode.needsScores());
+    this.similarity = searcher.getSimilarity();
     weights = new ArrayList<>();
     for (BooleanClause c : query) {
       Weight w = searcher.createWeight(c.getQuery(), c.isScoring() ? scoreMode : ScoreMode.COMPLETE_NO_SCORES, boost);

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/ExactPhraseScorer.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/ExactPhraseScorer.java b/lucene/core/src/java/org/apache/lucene/search/ExactPhraseScorer.java
index f4a7ca7..e2d6d80 100644
--- a/lucene/core/src/java/org/apache/lucene/search/ExactPhraseScorer.java
+++ b/lucene/core/src/java/org/apache/lucene/search/ExactPhraseScorer.java
@@ -22,7 +22,6 @@ import java.util.ArrayList;
 import java.util.List;
 
 import org.apache.lucene.index.PostingsEnum;
-import org.apache.lucene.search.similarities.Similarity;
 
 final class ExactPhraseScorer extends Scorer {
 
@@ -42,13 +41,13 @@ final class ExactPhraseScorer extends Scorer {
 
   private int freq;
 
-  private final Similarity.SimScorer docScorer;
+  private final LeafSimScorer docScorer;
   private final boolean needsScores, needsTotalHitCount;
   private float matchCost;
   private float minCompetitiveScore;
 
   ExactPhraseScorer(Weight weight, PhraseQuery.PostingsAndFreq[] postings,
-                    Similarity.SimScorer docScorer, ScoreMode scoreMode,
+                    LeafSimScorer docScorer, ScoreMode scoreMode,
                     float matchCost) throws IOException {
     super(weight);
     this.docScorer = docScorer;
@@ -123,7 +122,7 @@ final class ExactPhraseScorer extends Scorer {
 
   @Override
   public float maxScore() {
-    return docScorer.maxScore(Integer.MAX_VALUE);
+    return docScorer.maxScore();
   }
 
   /** Advance the given pos enum to the first doc on or after {@code target}.

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java b/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java
index 5ee815c..fc87563 100644
--- a/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java
+++ b/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java
@@ -32,7 +32,6 @@ import java.util.concurrent.Future;
 
 import org.apache.lucene.document.Document;
 import org.apache.lucene.index.DirectoryReader;
-import org.apache.lucene.index.FieldInvertState;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexReaderContext;
 import org.apache.lucene.index.IndexWriter;
@@ -75,36 +74,6 @@ import org.apache.lucene.util.ThreadInterruptedException;
  */
 public class IndexSearcher {
 
-  /** A search-time {@link Similarity} that does not make use of scoring factors
-   *  and may be used when scores are not needed. */
-  private static final Similarity NON_SCORING_SIMILARITY = new Similarity() {
-
-    @Override
-    public long computeNorm(FieldInvertState state) {
-      throw new UnsupportedOperationException("This Similarity may only be used for searching, not indexing");
-    }
-
-    @Override
-    public SimWeight computeWeight(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
-      return new SimWeight() {};
-    }
-
-    @Override
-    public SimScorer simScorer(SimWeight weight, LeafReaderContext context) throws IOException {
-      return new SimScorer() {
-        @Override
-        public float score(int doc, float freq) {
-          return 0f;
-        }
-        @Override
-        public float maxScore(float maxFreq) {
-          return 0f;
-        }
-      };
-    }
-
-  };
-
   private static QueryCache DEFAULT_QUERY_CACHE;
   private static QueryCachingPolicy DEFAULT_CACHING_POLICY = new UsageTrackingQueryCachingPolicy();
   static {
@@ -136,7 +105,7 @@ public class IndexSearcher {
    * Expert: returns a default Similarity instance.
    * In general, this method is only called to initialize searchers and writers.
    * User code and query implementations should respect
-   * {@link IndexSearcher#getSimilarity(boolean)}.
+   * {@link IndexSearcher#getSimilarity()}.
    * @lucene.internal
    */
   public static Similarity getDefaultSimilarity() {
@@ -329,15 +298,11 @@ public class IndexSearcher {
     this.similarity = similarity;
   }
 
-  /** Expert: Get the {@link Similarity} to use to compute scores. When
-   *  {@code needsScores} is {@code false}, this method will return a simple
-   *  {@link Similarity} that does not leverage scoring factors such as norms.
-   *  When {@code needsScores} is {@code true}, this returns the
+  /** Expert: Get the {@link Similarity} to use to compute scores. This returns the
    *  {@link Similarity} that has been set through {@link #setSimilarity(Similarity)}
-   *  or the {@link #getDefaultSimilarity()} default {@link Similarity} if none
-   *  has been set explicitly. */
-  public Similarity getSimilarity(boolean needsScores) {
-    return needsScores ? similarity : NON_SCORING_SIMILARITY;
+   *  or the default {@link Similarity} if none has been set explicitly. */
+  public Similarity getSimilarity() {
+    return similarity;
   }
 
   /**

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/LeafSimScorer.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/LeafSimScorer.java b/lucene/core/src/java/org/apache/lucene/search/LeafSimScorer.java
new file mode 100644
index 0000000..52b7d92
--- /dev/null
+++ b/lucene/core/src/java/org/apache/lucene/search/LeafSimScorer.java
@@ -0,0 +1,74 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.search;
+
+import java.io.IOException;
+
+import org.apache.lucene.index.LeafReader;
+import org.apache.lucene.index.NumericDocValues;
+import org.apache.lucene.search.similarities.Similarity.SimScorer;
+
+/**
+ * {@link SimScorer} on a specific {@link LeafReader}.
+ */
+public final class LeafSimScorer {
+
+  private final SimScorer scorer;
+  private final NumericDocValues norms;
+  private final float maxScore;
+
+  /**
+   * Sole constructor: Score documents of {@code reader} with {@code scorer}.
+   */
+  public LeafSimScorer(SimScorer scorer, LeafReader reader, boolean needsScores, float maxFreq) throws IOException {
+    this.scorer = scorer;
+    norms = needsScores ? reader.getNormValues(scorer.getField()) : null;
+    maxScore = scorer.maxScore(maxFreq);
+  }
+
+  private long getNormValue(int doc) throws IOException {
+    if (norms != null) {
+      boolean found = norms.advanceExact(doc);
+      assert found;
+      return norms.longValue();
+    } else {
+      return 1L; // default norm
+    }
+  }
+
+  /** Score the provided document assuming the given term document frequency.
+   *  This method must be called on non-decreasing sequences of doc ids.
+   *  @see SimScorer#score(float, long) */
+  public float score(int doc, float freq) throws IOException {
+    return scorer.score(freq, getNormValue(doc));
+  }
+
+  /** Explain the score for the provided document assuming the given term document frequency.
+   *  This method must be called on non-decreasing sequences of doc ids.
+   *  @see SimScorer#explain(Explanation, long) */
+  public Explanation explain(int doc, Explanation freqExpl) throws IOException {
+    return scorer.explain(freqExpl, getNormValue(doc));
+  }
+
+  /**
+   * Return an upper bound of the score.
+   * @see SimScorer#maxScore(float)
+   */
+  public float maxScore() {
+    return maxScore;
+  }
+}

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/MultiPhraseQuery.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/MultiPhraseQuery.java b/lucene/core/src/java/org/apache/lucene/search/MultiPhraseQuery.java
index 34361a7..941416e 100644
--- a/lucene/core/src/java/org/apache/lucene/search/MultiPhraseQuery.java
+++ b/lucene/core/src/java/org/apache/lucene/search/MultiPhraseQuery.java
@@ -18,19 +18,26 @@ package org.apache.lucene.search;
 
 
 import java.io.IOException;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
 
-import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.index.LeafReader;
-import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexReaderContext;
+import org.apache.lucene.index.LeafReader;
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.index.TermContext;
 import org.apache.lucene.index.TermState;
 import org.apache.lucene.index.Terms;
 import org.apache.lucene.index.TermsEnum;
-import org.apache.lucene.search.similarities.Similarity.SimScorer;
 import org.apache.lucene.search.similarities.Similarity;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
@@ -183,7 +190,7 @@ public class MultiPhraseQuery extends Query {
 
   private class MultiPhraseWeight extends Weight {
     private final Similarity similarity;
-    private final Similarity.SimWeight stats;
+    private final Similarity.SimScorer stats;
     private final Map<Term,TermContext> termContexts = new HashMap<>();
     private final ScoreMode scoreMode;
 
@@ -191,7 +198,7 @@ public class MultiPhraseQuery extends Query {
       throws IOException {
       super(MultiPhraseQuery.this);
       this.scoreMode = scoreMode;
-      this.similarity = searcher.getSimilarity(scoreMode.needsScores());
+      this.similarity = searcher.getSimilarity();
       final IndexReaderContext context = searcher.getTopReaderContext();
 
       // compute idf
@@ -212,7 +219,7 @@ public class MultiPhraseQuery extends Query {
       if (allTermStats.isEmpty()) {
         stats = null; // none of the terms were found, we won't use sim at all
       } else {
-        stats = similarity.computeWeight(
+        stats = similarity.scorer(
           boost,
           searcher.collectionStatistics(field),
           allTermStats.toArray(new TermStatistics[allTermStats.size()]));
@@ -282,11 +289,11 @@ public class MultiPhraseQuery extends Query {
 
       if (slop == 0) {
         return new ExactPhraseScorer(this, postingsFreqs,
-                                      similarity.simScorer(stats, context),
+                                      new LeafSimScorer(stats, context.reader(), scoreMode.needsScores(), Integer.MAX_VALUE),
                                       scoreMode, totalMatchCost);
       } else {
         return new SloppyPhraseScorer(this, postingsFreqs, slop,
-                                        similarity.simScorer(stats, context),
+                                        new LeafSimScorer(stats, context.reader(), scoreMode.needsScores(), Float.POSITIVE_INFINITY),
                                         scoreMode.needsScores(), totalMatchCost);
       }
     }
@@ -303,7 +310,7 @@ public class MultiPhraseQuery extends Query {
         int newDoc = scorer.iterator().advance(doc);
         if (newDoc == doc) {
           float freq = slop == 0 ? ((ExactPhraseScorer)scorer).freq() : ((SloppyPhraseScorer)scorer).sloppyFreq();
-          SimScorer docScorer = similarity.simScorer(stats, context);
+          LeafSimScorer docScorer = new LeafSimScorer(stats, context.reader(), scoreMode.needsScores(), Float.POSITIVE_INFINITY);
           Explanation freqExplanation = Explanation.match(freq, "phraseFreq=" + freq);
           Explanation scoreExplanation = docScorer.explain(doc, freqExplanation);
           return Explanation.match(

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/PhraseQuery.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/PhraseQuery.java b/lucene/core/src/java/org/apache/lucene/search/PhraseQuery.java
index 3d359b4..295cc90 100644
--- a/lucene/core/src/java/org/apache/lucene/search/PhraseQuery.java
+++ b/lucene/core/src/java/org/apache/lucene/search/PhraseQuery.java
@@ -37,7 +37,6 @@ import org.apache.lucene.index.TermState;
 import org.apache.lucene.index.Terms;
 import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.search.similarities.Similarity;
-import org.apache.lucene.search.similarities.Similarity.SimScorer;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
 
@@ -352,7 +351,7 @@ public class PhraseQuery extends Query {
 
   private class PhraseWeight extends Weight {
     private final Similarity similarity;
-    private final Similarity.SimWeight stats;
+    private final Similarity.SimScorer stats;
     private final ScoreMode scoreMode;
     private transient TermContext states[];
 
@@ -366,7 +365,7 @@ public class PhraseQuery extends Query {
         throw new IllegalStateException("PhraseWeight requires that the first position is 0, call rewrite first");
       }
       this.scoreMode = scoreMode;
-      this.similarity = searcher.getSimilarity(scoreMode.needsScores());
+      this.similarity = searcher.getSimilarity();
       final IndexReaderContext context = searcher.getTopReaderContext();
       states = new TermContext[terms.length];
       TermStatistics termStats[] = new TermStatistics[terms.length];
@@ -380,7 +379,7 @@ public class PhraseQuery extends Query {
         }
       }
       if (termUpTo > 0) {
-        stats = similarity.computeWeight(boost, searcher.collectionStatistics(field), Arrays.copyOf(termStats, termUpTo));
+        stats = similarity.scorer(boost, searcher.collectionStatistics(field), Arrays.copyOf(termStats, termUpTo));
       } else {
         stats = null; // no terms at all, we won't use similarity
       }
@@ -433,11 +432,11 @@ public class PhraseQuery extends Query {
 
       if (slop == 0) {  // optimize exact case
         return new ExactPhraseScorer(this, postingsFreqs,
-                                      similarity.simScorer(stats, context),
+                                      new LeafSimScorer(stats, context.reader(), scoreMode.needsScores(), Integer.MAX_VALUE),
                                       scoreMode, totalMatchCost);
       } else {
         return new SloppyPhraseScorer(this, postingsFreqs, slop,
-                                        similarity.simScorer(stats, context),
+                                        new LeafSimScorer(stats, context.reader(), scoreMode.needsScores(), Float.POSITIVE_INFINITY),
                                         scoreMode.needsScores(), totalMatchCost);
       }
     }
@@ -459,7 +458,7 @@ public class PhraseQuery extends Query {
         int newDoc = scorer.iterator().advance(doc);
         if (newDoc == doc) {
           float freq = slop == 0 ? ((ExactPhraseScorer)scorer).freq() : ((SloppyPhraseScorer)scorer).sloppyFreq();
-          SimScorer docScorer = similarity.simScorer(stats, context);
+          LeafSimScorer docScorer = new LeafSimScorer(stats, context.reader(), scoreMode.needsScores(), Float.POSITIVE_INFINITY);
           Explanation freqExplanation = Explanation.match(freq, "phraseFreq=" + freq);
           Explanation scoreExplanation = docScorer.explain(doc, freqExplanation);
           return Explanation.match(

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/SloppyPhraseScorer.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/SloppyPhraseScorer.java b/lucene/core/src/java/org/apache/lucene/search/SloppyPhraseScorer.java
index dc5490a..60b77c5 100644
--- a/lucene/core/src/java/org/apache/lucene/search/SloppyPhraseScorer.java
+++ b/lucene/core/src/java/org/apache/lucene/search/SloppyPhraseScorer.java
@@ -26,7 +26,6 @@ import java.util.HashSet;
 import java.util.LinkedHashMap;
 
 import org.apache.lucene.index.Term;
-import org.apache.lucene.search.similarities.Similarity;
 import org.apache.lucene.util.FixedBitSet;
 
 final class SloppyPhraseScorer extends Scorer {
@@ -36,7 +35,7 @@ final class SloppyPhraseScorer extends Scorer {
 
   private float sloppyFreq; //phrase frequency in current doc as computed by phraseFreq().
 
-  private final Similarity.SimScorer docScorer;
+  private final LeafSimScorer docScorer;
   
   private final int slop;
   private final int numPostings;
@@ -55,7 +54,7 @@ final class SloppyPhraseScorer extends Scorer {
   private final float matchCost;
   
   SloppyPhraseScorer(Weight weight, PhraseQuery.PostingsAndFreq[] postings,
-      int slop, Similarity.SimScorer docScorer, boolean needsScores,
+      int slop, LeafSimScorer docScorer, boolean needsScores,
       float matchCost) {
     super(weight);
     this.docScorer = docScorer;
@@ -558,7 +557,7 @@ final class SloppyPhraseScorer extends Scorer {
 
   @Override
   public float maxScore() {
-    return docScorer.maxScore(Float.POSITIVE_INFINITY);
+    return docScorer.maxScore();
   }
 
   @Override

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/SynonymQuery.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/SynonymQuery.java b/lucene/core/src/java/org/apache/lucene/search/SynonymQuery.java
index ce9d6e0..3f4c06d 100644
--- a/lucene/core/src/java/org/apache/lucene/search/SynonymQuery.java
+++ b/lucene/core/src/java/org/apache/lucene/search/SynonymQuery.java
@@ -35,7 +35,6 @@ import org.apache.lucene.index.TermContext;
 import org.apache.lucene.index.TermState;
 import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.search.similarities.Similarity;
-import org.apache.lucene.search.similarities.Similarity.SimScorer;
 import org.apache.lucene.util.BytesRef;
 
 /**
@@ -129,7 +128,7 @@ public final class SynonymQuery extends Query {
   class SynonymWeight extends Weight {
     private final TermContext termContexts[];
     private final Similarity similarity;
-    private final Similarity.SimWeight simWeight;
+    private final Similarity.SimScorer simWeight;
 
     SynonymWeight(Query query, IndexSearcher searcher, float boost) throws IOException {
       super(query);
@@ -145,10 +144,10 @@ public final class SynonymQuery extends Query {
           totalTermFreq += termStats.totalTermFreq();
         }
       }
-      this.similarity = searcher.getSimilarity(true);
+      this.similarity = searcher.getSimilarity();
       if (docFreq > 0) {
         TermStatistics pseudoStats = new TermStatistics(new BytesRef("synonym pseudo-term"), docFreq, totalTermFreq);
-        this.simWeight = similarity.computeWeight(boost, collectionStats, pseudoStats);
+        this.simWeight = similarity.scorer(boost, collectionStats, pseudoStats);
       } else {
         this.simWeight = null; // no terms exist at all, we won't use similarity
       }
@@ -175,7 +174,7 @@ public final class SynonymQuery extends Query {
             assert scorer instanceof TermScorer;
             freq = ((TermScorer)scorer).freq();
           }
-          SimScorer docScorer = similarity.simScorer(simWeight, context);
+          LeafSimScorer docScorer = new LeafSimScorer(simWeight, context.reader(), true, Float.POSITIVE_INFINITY);
           Explanation freqExplanation = Explanation.match(freq, "termFreq=" + freq);
           Explanation scoreExplanation = docScorer.explain(doc, freqExplanation);
           return Explanation.match(
@@ -190,7 +189,6 @@ public final class SynonymQuery extends Query {
 
     @Override
     public Scorer scorer(LeafReaderContext context) throws IOException {
-      Similarity.SimScorer simScorer = null;
       IndexOptions indexOptions = IndexOptions.NONE;
       if (terms.length > 0) {
         FieldInfo info = context.reader()
@@ -202,21 +200,17 @@ public final class SynonymQuery extends Query {
       }
       // we use termscorers + disjunction as an impl detail
       List<Scorer> subScorers = new ArrayList<>();
-      long maxFreq = 0;
+      long totalMaxFreq = 0;
       for (int i = 0; i < terms.length; i++) {
         TermState state = termContexts[i].get(context.ord);
         if (state != null) {
           TermsEnum termsEnum = context.reader().terms(terms[i].field()).iterator();
           termsEnum.seekExact(terms[i].bytes(), state);
-
-          maxFreq += getMaxFreq(indexOptions, termsEnum.totalTermFreq(), termsEnum.docFreq());
-
+          long termMaxFreq = getMaxFreq(indexOptions, termsEnum.totalTermFreq(), termsEnum.docFreq());
+          totalMaxFreq += termMaxFreq;
           PostingsEnum postings = termsEnum.postings(null, PostingsEnum.FREQS);
-          // lazy init sim, in case no terms exist
-          if (simScorer == null) {
-            simScorer = similarity.simScorer(simWeight, context);
-          }
-          subScorers.add(new TermScorer(this, postings, simScorer, Float.POSITIVE_INFINITY));
+          LeafSimScorer simScorer = new LeafSimScorer(simWeight, context.reader(), true, termMaxFreq);
+          subScorers.add(new TermScorer(this, postings, simScorer));
         }
       }
       if (subScorers.isEmpty()) {
@@ -225,7 +219,8 @@ public final class SynonymQuery extends Query {
         // we must optimize this case (term not in segment), disjunctionscorer requires >= 2 subs
         return subScorers.get(0);
       } else {
-        return new SynonymScorer(simScorer, this, subScorers, maxFreq);
+        LeafSimScorer simScorer = new LeafSimScorer(simWeight, context.reader(), true, totalMaxFreq);
+        return new SynonymScorer(simScorer, this, subScorers);
       }
     }
 
@@ -248,13 +243,11 @@ public final class SynonymQuery extends Query {
   }
 
   static class SynonymScorer extends DisjunctionScorer {
-    private final Similarity.SimScorer similarity;
-    private final float maxFreq;
+    private final LeafSimScorer similarity;
     
-    SynonymScorer(Similarity.SimScorer similarity, Weight weight, List<Scorer> subScorers, float maxFreq) {
+    SynonymScorer(LeafSimScorer similarity, Weight weight, List<Scorer> subScorers) {
       super(weight, subScorers, true);
       this.similarity = similarity;
-      this.maxFreq = maxFreq;
     }
 
     @Override
@@ -264,7 +257,7 @@ public final class SynonymQuery extends Query {
 
     @Override
     public float maxScore() {
-      return similarity.maxScore(maxFreq);
+      return similarity.maxScore();
     }
 
     /** combines TF of all subs. */

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/TermQuery.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/TermQuery.java b/lucene/core/src/java/org/apache/lucene/search/TermQuery.java
index 925fe93..3fa465d 100644
--- a/lucene/core/src/java/org/apache/lucene/search/TermQuery.java
+++ b/lucene/core/src/java/org/apache/lucene/search/TermQuery.java
@@ -33,7 +33,6 @@ import org.apache.lucene.index.TermState;
 import org.apache.lucene.index.Terms;
 import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.search.similarities.Similarity;
-import org.apache.lucene.search.similarities.Similarity.SimScorer;
 
 /**
  * A Query that matches documents containing a term. This may be combined with
@@ -46,7 +45,7 @@ public class TermQuery extends Query {
 
   final class TermWeight extends Weight {
     private final Similarity similarity;
-    private final Similarity.SimWeight stats;
+    private final Similarity.SimScorer simScorer;
     private final TermContext termStates;
     private final boolean needsScores;
 
@@ -58,7 +57,7 @@ public class TermQuery extends Query {
       }
       this.needsScores = needsScores;
       this.termStates = termStates;
-      this.similarity = searcher.getSimilarity(needsScores);
+      this.similarity = searcher.getSimilarity();
 
       final CollectionStatistics collectionStats;
       final TermStatistics termStats;
@@ -72,9 +71,9 @@ public class TermQuery extends Query {
       }
      
       if (termStats == null) {
-        this.stats = null; // term doesn't exist in any segment, we won't use similarity at all
+        this.simScorer = null; // term doesn't exist in any segment, we won't use similarity at all
       } else {
-        this.stats = similarity.computeWeight(boost, collectionStats, termStats);
+        this.simScorer = similarity.scorer(boost, collectionStats, termStats);
       }
     }
 
@@ -101,8 +100,8 @@ public class TermQuery extends Query {
           .getIndexOptions();
       PostingsEnum docs = termsEnum.postings(null, needsScores ? PostingsEnum.FREQS : PostingsEnum.NONE);
       assert docs != null;
-      return new TermScorer(this, docs, similarity.simScorer(stats, context),
-          getMaxFreq(indexOptions, termsEnum.totalTermFreq(), termsEnum.docFreq()));
+      float maxFreq = getMaxFreq(indexOptions, termsEnum.totalTermFreq(), termsEnum.docFreq());
+      return new TermScorer(this, docs, new LeafSimScorer(simScorer, context.reader(), needsScores, maxFreq));
     }
 
     private long getMaxFreq(IndexOptions indexOptions, long ttf, long df) {
@@ -166,7 +165,7 @@ public class TermQuery extends Query {
         int newDoc = scorer.iterator().advance(doc);
         if (newDoc == doc) {
           float freq = scorer.freq();
-          SimScorer docScorer = similarity.simScorer(stats, context);
+          LeafSimScorer docScorer = new LeafSimScorer(simScorer, context.reader(), true, Integer.MAX_VALUE);
           Explanation freqExplanation = Explanation.match(freq, "freq, occurrences of term within document");
           Explanation scoreExplanation = docScorer.explain(doc, freqExplanation);
           return Explanation.match(

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/TermScorer.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/TermScorer.java b/lucene/core/src/java/org/apache/lucene/search/TermScorer.java
index a4aeb04..653a60e 100644
--- a/lucene/core/src/java/org/apache/lucene/search/TermScorer.java
+++ b/lucene/core/src/java/org/apache/lucene/search/TermScorer.java
@@ -20,14 +20,12 @@ package org.apache.lucene.search;
 import java.io.IOException;
 
 import org.apache.lucene.index.PostingsEnum;
-import org.apache.lucene.search.similarities.Similarity;
 
 /** Expert: A <code>Scorer</code> for documents matching a <code>Term</code>.
  */
 final class TermScorer extends Scorer {
   private final PostingsEnum postingsEnum;
-  private final Similarity.SimScorer docScorer;
-  private final float maxFreq;
+  private final LeafSimScorer docScorer;
 
   /**
    * Construct a <code>TermScorer</code>.
@@ -39,14 +37,11 @@ final class TermScorer extends Scorer {
    * @param docScorer
    *          The <code>Similarity.SimScorer</code> implementation
    *          to be used for score computations.
-   * @param maxFreq
-   *          An upper bound of the term frequency of the searched term in any document.
    */
-  TermScorer(Weight weight, PostingsEnum td, Similarity.SimScorer docScorer, float maxFreq) {
+  TermScorer(Weight weight, PostingsEnum td, LeafSimScorer docScorer) {
     super(weight);
     this.docScorer = docScorer;
     this.postingsEnum = td;
-    this.maxFreq = maxFreq;
   }
 
   @Override
@@ -71,7 +66,7 @@ final class TermScorer extends Scorer {
 
   @Override
   public float maxScore() {
-    return docScorer.maxScore(maxFreq);
+    return docScorer.maxScore();
   }
 
   /** Returns a string representation of this <code>TermScorer</code>. */

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/package-info.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/package-info.java b/lucene/core/src/java/org/apache/lucene/search/package-info.java
index 69c5c2a..7e53da4 100644
--- a/lucene/core/src/java/org/apache/lucene/search/package-info.java
+++ b/lucene/core/src/java/org/apache/lucene/search/package-info.java
@@ -378,7 +378,7 @@
  *                 scored the way it was.
  *                 Typically a weight such as TermWeight
  *                 that scores via a {@link org.apache.lucene.search.similarities.Similarity Similarity} will make use of the Similarity's implementation:
- *                 {@link org.apache.lucene.search.similarities.Similarity.SimScorer#explain(int, Explanation) SimScorer#explain(int doc, Explanation freq)}.
+ *                 {@link org.apache.lucene.search.similarities.Similarity.SimScorer#explain(Explanation, long) SimScorer#explain(Explanation freq, long norm)}.
  *             </li>
  *         </ol>
  * <a name="scorerClass"></a>
@@ -402,7 +402,7 @@
  *                 {@link org.apache.lucene.search.Scorer#score score()} &mdash; Return the score of the
  *                 current document. This value can be determined in any appropriate way for an application. For instance, the
  *                 {@link org.apache.lucene.search.TermScorer TermScorer} simply defers to the configured Similarity:
- *                 {@link org.apache.lucene.search.similarities.Similarity.SimScorer#score(int, float) SimScorer.score(int doc, float freq)}.
+ *                 {@link org.apache.lucene.search.similarities.Similarity.SimScorer#score(float, long) SimScorer.score(float freq, long norm)}.
  *             </li>
  *             <li>
  *                 {@link org.apache.lucene.search.Scorer#getChildren getChildren()} &mdash; Returns any child subscorers

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/Axiomatic.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/Axiomatic.java b/lucene/core/src/java/org/apache/lucene/search/similarities/Axiomatic.java
index 1522e5d..3865933 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/Axiomatic.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/Axiomatic.java
@@ -120,10 +120,10 @@ public abstract class Axiomatic extends SimilarityBase {
 
   @Override
   protected Explanation explain(
-      BasicStats stats, int doc, Explanation freq, double docLen) {    
+      BasicStats stats, Explanation freq, double docLen) {    
     List<Explanation> subs = new ArrayList<>();
     double f = freq.getValue().doubleValue();
-    explain(subs, stats, doc, f, docLen);
+    explain(subs, stats, f, docLen);
     
     double score = tf(stats, f, docLen)
         * ln(stats, f, docLen)
@@ -132,7 +132,7 @@ public abstract class Axiomatic extends SimilarityBase {
         - gamma(stats, f, docLen);
 
     Explanation explanation = Explanation.match((float) score,
-        "score(" + getClass().getSimpleName() + ", doc=" + doc + ", freq=" + freq.getValue() +"), computed from:",
+        "score(" + getClass().getSimpleName() + ", freq=" + freq.getValue() +"), computed from:",
         subs);
     if (stats.boost != 1f) {
       explanation = Explanation.match((float) (score * stats.boost), "Boosted score, computed as (score * boost) from:",
@@ -148,7 +148,7 @@ public abstract class Axiomatic extends SimilarityBase {
   }
 
   @Override
-  protected void explain(List<Explanation> subs, BasicStats stats, int doc,
+  protected void explain(List<Explanation> subs, BasicStats stats,
                          double freq, double docLen) {
     if (stats.getBoost() != 1.0d) {
       subs.add(Explanation.match((float) stats.getBoost(),
@@ -165,7 +165,7 @@ public abstract class Axiomatic extends SimilarityBase {
     subs.add(tflnExplain(stats, freq, docLen));
     subs.add(idfExplain(stats, freq, docLen));
     subs.add(Explanation.match((float) gamma(stats, freq, docLen), "gamma"));
-    super.explain(subs, stats, doc, freq, docLen);
+    super.explain(subs, stats, freq, docLen);
   }
 
   /**

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/BM25Similarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/BM25Similarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/BM25Similarity.java
index dce156b..09bef40 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/BM25Similarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/BM25Similarity.java
@@ -22,8 +22,6 @@ import java.util.ArrayList;
 import java.util.List;
 
 import org.apache.lucene.index.FieldInvertState;
-import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.search.CollectionStatistics;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.TermStatistics;
@@ -176,7 +174,7 @@ public class BM25Similarity extends Similarity {
   }
 
   @Override
-  public final SimWeight computeWeight(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
+  public final SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
     Explanation idf = termStats.length == 1 ? idfExplain(collectionStats, termStats[0]) : idfExplain(collectionStats, termStats);
     float avgdl = avgFieldLength(collectionStats);
 
@@ -184,100 +182,17 @@ public class BM25Similarity extends Similarity {
     for (int i = 0; i < cache.length; i++) {
       cache[i] = k1 * ((1 - b) + b * LENGTH_TABLE[i] / avgdl);
     }
-    return new BM25Stats(collectionStats.field(), boost, k1, idf, avgdl, cache);
-  }
-
-  @Override
-  public final SimScorer simScorer(SimWeight stats, LeafReaderContext context) throws IOException {
-    BM25Stats bm25stats = (BM25Stats) stats;
-    return new BM25DocScorer(bm25stats, context.reader().getNormValues(bm25stats.field));
-  }
-  
-  private class BM25DocScorer extends SimScorer {
-    private final BM25Stats stats;
-    private final float weightValue; // boost * idf * (k1 + 1)
-    private final NumericDocValues norms;
-    /** precomputed cache for all length values */
-    private final float[] lengthCache;
-    /** precomputed norm[256] with k1 * ((1 - b) + b * dl / avgdl) */
-    private final float[] cache;
-    
-    BM25DocScorer(BM25Stats stats, NumericDocValues norms) throws IOException {
-      this.stats = stats;
-      this.weightValue = stats.weight;
-      this.norms = norms;
-      lengthCache = LENGTH_TABLE;
-      cache = stats.cache;
-    }
-    
-    @Override
-    public float score(int doc, float freq) throws IOException {
-      // if there are no norms, we act as if b=0
-      double norm;
-      if (norms == null) {
-        norm = k1;
-      } else {
-        boolean found = norms.advanceExact(doc);
-        assert found;
-        norm = cache[((byte) norms.longValue()) & 0xFF];
-      }
-      return weightValue * (float) (freq / (freq + norm));
-    }
-
-    @Override
-    public float maxScore(float maxFreq) {
-      // TODO: leverage maxFreq and the min norm from the cache
-      return weightValue;
-    }
-
-    @Override
-    public Explanation explain(int doc, Explanation freq) throws IOException {
-      List<Explanation> subs = new ArrayList<>();
-      subs.addAll(stats.explain());
-      Explanation tfExpl = explainTF(doc, freq);
-      subs.add(tfExpl);
-      return Explanation.match(stats.weight * tfExpl.getValue().floatValue(),
-          "score(doc="+doc+",freq="+freq.getValue()+"), product of:", subs);
-    }
-    
-    private Explanation explainTF(int doc, Explanation freq) throws IOException {
-      List<Explanation> subs = new ArrayList<>();
-      subs.add(freq);
-      subs.add(Explanation.match(k1, "k1, term saturation parameter"));
-      if (norms == null) {
-        subs.add(Explanation.match(0, "b, field omits length norms"));
-        return Explanation.match(
-            (float) (freq.getValue().floatValue() / (freq.getValue().floatValue() + (double) k1)),
-            "tf, computed as freq / (freq + k1) from:", subs);
-      } else {
-        boolean found = norms.advanceExact(doc);
-        assert found;
-        byte norm = (byte) norms.longValue();
-        float doclen = lengthCache[norm & 0xff];
-        subs.add(Explanation.match(b, "b, length normalization parameter"));
-        if ((norm & 0xFF) > 39) {
-          subs.add(Explanation.match(doclen, "dl, length of field (approximate)"));
-        } else {
-          subs.add(Explanation.match(doclen, "dl, length of field"));
-        }
-        subs.add(Explanation.match(stats.avgdl, "avgdl, average length of field"));
-        float normValue = k1 * ((1 - b) + b * doclen / stats.avgdl);
-        return Explanation.match(
-            (float) (freq.getValue().floatValue() / (freq.getValue().floatValue() + (double) normValue)),
-            "tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl)) from:", subs);
-      }
-    }
-
+    return new BM25Scorer(collectionStats.field(), boost, k1, b, idf, avgdl, cache);
   }
   
   /** Collection statistics for the BM25 model. */
-  private static class BM25Stats extends SimWeight {
-    /** field name, for pulling norms */
-    private final String field;
+  private static class BM25Scorer extends SimScorer {
     /** query boost */
     private final float boost;
     /** k1 value for scale factor */
     private final float k1;
+    /** b value for length normalization impact */
+    private final float b;
     /** BM25's idf */
     private final Explanation idf;
     /** The average document length. */
@@ -287,17 +202,57 @@ public class BM25Similarity extends Similarity {
     /** weight (idf * boost) */
     private final float weight;
 
-    BM25Stats(String field, float boost, float k1, Explanation idf, float avgdl, float[] cache) {
-      this.field = field;
+    BM25Scorer(String field, float boost, float k1, float b, Explanation idf, float avgdl, float[] cache) {
+      super(field);
       this.boost = boost;
       this.idf = idf;
       this.avgdl = avgdl;
       this.k1 = k1;
+      this.b = b;
       this.cache = cache;
       this.weight = (k1 + 1) * boost * idf.getValue().floatValue();
     }
 
-    private List<Explanation> explain() {
+    @Override
+    public float score(float freq, long encodedNorm) throws IOException {
+      double norm = cache[((byte) encodedNorm) & 0xFF];
+      return weight * (float) (freq / (freq + norm));
+    }
+
+    @Override
+    public float maxScore(float maxFreq) {
+      // TODO: leverage maxFreq and the min norm from the cache
+      return weight;
+    }
+
+    @Override
+    public Explanation explain(Explanation freq, long encodedNorm) throws IOException {
+      List<Explanation> subs = new ArrayList<>(explainConstantFactors());
+      Explanation tfExpl = explainTF(freq, encodedNorm);
+      subs.add(tfExpl);
+      return Explanation.match(weight * tfExpl.getValue().floatValue(),
+          "score(freq="+freq.getValue()+"), product of:", subs);
+    }
+    
+    private Explanation explainTF(Explanation freq, long norm) throws IOException {
+      List<Explanation> subs = new ArrayList<>();
+      subs.add(freq);
+      subs.add(Explanation.match(k1, "k1, term saturation parameter"));
+      float doclen = LENGTH_TABLE[((byte) norm) & 0xff];
+      subs.add(Explanation.match(b, "b, length normalization parameter"));
+      if ((norm & 0xFF) > 39) {
+        subs.add(Explanation.match(doclen, "dl, length of field (approximate)"));
+      } else {
+        subs.add(Explanation.match(doclen, "dl, length of field"));
+      }
+      subs.add(Explanation.match(avgdl, "avgdl, average length of field"));
+      float normValue = k1 * ((1 - b) + b * doclen / avgdl);
+      return Explanation.match(
+          (float) (freq.getValue().floatValue() / (freq.getValue().floatValue() + (double) normValue)),
+          "tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl)) from:", subs);
+    }
+
+    private List<Explanation> explainConstantFactors() {
       List<Explanation> subs = new ArrayList<>();
       // scale factor
       subs.add(Explanation.match(k1 + 1, "scaling factor, k1 + 1"));
@@ -311,7 +266,6 @@ public class BM25Similarity extends Similarity {
     }
   }
 
-
   @Override
   public String toString() {
     return "BM25(k1=" + k1 + ",b=" + b + ")";

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/BasicStats.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/BasicStats.java b/lucene/core/src/java/org/apache/lucene/search/similarities/BasicStats.java
index cc3cab4..dc9356f 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/BasicStats.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/BasicStats.java
@@ -23,7 +23,7 @@ import org.apache.lucene.index.Terms;
  * Stores all statistics commonly used ranking methods.
  * @lucene.experimental
  */
-public class BasicStats extends Similarity.SimWeight {
+public class BasicStats {
   final String field;
   /** The number of documents. */
   protected long numberOfDocuments;

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/BooleanSimilarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/BooleanSimilarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/BooleanSimilarity.java
index 7134172..2690365 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/BooleanSimilarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/BooleanSimilarity.java
@@ -19,7 +19,6 @@ package org.apache.lucene.search.similarities;
 import java.io.IOException;
 
 import org.apache.lucene.index.FieldInvertState;
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.CollectionStatistics;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.TermStatistics;
@@ -47,44 +46,36 @@ public class BooleanSimilarity extends Similarity {
   }
 
   @Override
-  public SimWeight computeWeight(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
-    return new BooleanWeight(boost);
+  public SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
+    return new BooleanWeight(collectionStats.field(), boost);
   }
 
-  private static class BooleanWeight extends SimWeight {
+  private static class BooleanWeight extends SimScorer {
     final float boost;
 
-    BooleanWeight(float boost) {
+    BooleanWeight(String field, float boost) {
+      super(field);
       this.boost = boost;
     }
-  }
-
-  @Override
-  public SimScorer simScorer(SimWeight weight, LeafReaderContext context) throws IOException {
-    final float boost = ((BooleanWeight) weight).boost;
-
-    return new SimScorer() {
 
-      @Override
-      public float score(int doc, float freq) throws IOException {
-        return boost;
-      }
-
-      @Override
-      public float maxScore(float maxFreq) {
-        return boost;
-      }
+    @Override
+    public float score(float freq, long norm) throws IOException {
+      return boost;
+    }
 
-      @Override
-      public Explanation explain(int doc, Explanation freq) throws IOException {
-        Explanation queryBoostExpl = Explanation.match(boost, "boost, query boost");
-        return Explanation.match(
-            queryBoostExpl.getValue(),
-            "score(" + getClass().getSimpleName() + ", doc=" + doc + "), computed from:",
-            queryBoostExpl);
-      }
+    @Override
+    public float maxScore(float maxFreq) {
+      return boost;
+    }
 
-    };
+    @Override
+    public Explanation explain(Explanation freq, long norm) throws IOException {
+      Explanation queryBoostExpl = Explanation.match(boost, "boost, query boost");
+      return Explanation.match(
+          queryBoostExpl.getValue(),
+          "score(" + getClass().getSimpleName() + "), computed from:",
+          queryBoostExpl);
+    }
   }
 
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/DFISimilarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/DFISimilarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/DFISimilarity.java
index 66f22be..44da93c 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/DFISimilarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/DFISimilarity.java
@@ -79,12 +79,12 @@ public class DFISimilarity extends SimilarityBase {
 
   @Override
   protected Explanation explain(
-      BasicStats stats, int doc, Explanation freq, double docLen) {
+      BasicStats stats, Explanation freq, double docLen) {
     final double expected = (stats.getTotalTermFreq() + 1) * docLen /
         (stats.getNumberOfFieldTokens() + 1);
     if (freq.getValue().doubleValue() <= expected){
       return Explanation.match((float) 0, "score(" +
-          getClass().getSimpleName() + ", doc=" + doc + ", freq=" +
+          getClass().getSimpleName() + ", freq=" +
           freq.getValue() +"), equals to 0");
     }
     Explanation explExpected = Explanation.match((float) expected,
@@ -103,7 +103,7 @@ public class DFISimilarity extends SimilarityBase {
 
     return Explanation.match(
         (float) score(stats, freq.getValue().doubleValue(), docLen),
-        "score(" + getClass().getSimpleName() + ", doc=" + doc + ", freq=" +
+        "score(" + getClass().getSimpleName() + ", freq=" +
             freq.getValue() +"), computed as boost * log2(measure + 1) from:",
         Explanation.match( (float)stats.getBoost(), "boost, query boost"),
         explMeasure);

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/DFRSimilarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/DFRSimilarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/DFRSimilarity.java
index a41e35c..1677168 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/DFRSimilarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/DFRSimilarity.java
@@ -121,7 +121,7 @@ public class DFRSimilarity extends SimilarityBase {
 
   @Override
   protected void explain(List<Explanation> subs,
-      BasicStats stats, int doc, double freq, double docLen) {
+      BasicStats stats, double freq, double docLen) {
     if (stats.getBoost() != 1.0d) {
       subs.add(Explanation.match( (float)stats.getBoost(), "boost, query boost"));
     }
@@ -136,13 +136,13 @@ public class DFRSimilarity extends SimilarityBase {
 
   @Override
   protected Explanation explain(
-      BasicStats stats, int doc, Explanation freq, double docLen) {
+      BasicStats stats, Explanation freq, double docLen) {
     List<Explanation> subs = new ArrayList<>();
-    explain(subs, stats, doc, freq.getValue().doubleValue(), docLen);
+    explain(subs, stats, freq.getValue().doubleValue(), docLen);
 
     return Explanation.match(
         (float) score(stats, freq.getValue().doubleValue(), docLen),
-        "score(" + getClass().getSimpleName() + ", doc=" + doc + ", freq=" +
+        "score(" + getClass().getSimpleName() + ", freq=" +
             freq.getValue() +"), computed as boost * " +
             "basicModel.score(stats, tfn) * afterEffect.score(stats, tfn) from:",
         subs);

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/IBSimilarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/IBSimilarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/IBSimilarity.java
index 9a57608..231d554 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/IBSimilarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/IBSimilarity.java
@@ -112,7 +112,7 @@ public class IBSimilarity extends SimilarityBase {
 
   @Override
   protected void explain(
-      List<Explanation> subs, BasicStats stats, int doc, double freq, double docLen) {
+      List<Explanation> subs, BasicStats stats, double freq, double docLen) {
     if (stats.getBoost() != 1.0d) {
       subs.add(Explanation.match((float)stats.getBoost(), "boost, query boost"));
     }
@@ -125,13 +125,13 @@ public class IBSimilarity extends SimilarityBase {
 
   @Override
   protected Explanation explain(
-      BasicStats stats, int doc, Explanation freq, double docLen) {
+      BasicStats stats, Explanation freq, double docLen) {
     List<Explanation> subs = new ArrayList<>();
-    explain(subs, stats, doc, freq.getValue().doubleValue(), docLen);
+    explain(subs, stats, freq.getValue().doubleValue(), docLen);
 
     return Explanation.match(
         (float) score(stats, freq.getValue().doubleValue(), docLen),
-        "score(" + getClass().getSimpleName() + ", doc=" + doc + ", freq=" +
+        "score(" + getClass().getSimpleName() + ", freq=" +
             freq.getValue() +"), computed as boost * " +
             "distribution.score(stats, normalization.tfn(stats, freq," +
             " docLen), lambda.lambda(stats)) from:",

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/LMDirichletSimilarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/LMDirichletSimilarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/LMDirichletSimilarity.java
index c12cba4..7522c17 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/LMDirichletSimilarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/LMDirichletSimilarity.java
@@ -84,7 +84,7 @@ public class LMDirichletSimilarity extends LMSimilarity {
   }
 
   @Override
-  protected void explain(List<Explanation> subs, BasicStats stats, int doc,
+  protected void explain(List<Explanation> subs, BasicStats stats,
       double freq, double docLen) {
     if (stats.getBoost() != 1.0d) {
       subs.add(Explanation.match((float) stats.getBoost(), "query boost"));
@@ -107,18 +107,18 @@ public class LMDirichletSimilarity extends LMSimilarity {
         (float)Math.log(mu / (docLen + mu)),
         "document norm, computed as log(mu / (dl + mu))"));
     subs.add(Explanation.match((float) docLen,"dl, length of field"));
-    super.explain(subs, stats, doc, freq, docLen);
+    super.explain(subs, stats, freq, docLen);
   }
 
   @Override
   protected Explanation explain(
-      BasicStats stats, int doc, Explanation freq, double docLen) {
+      BasicStats stats, Explanation freq, double docLen) {
     List<Explanation> subs = new ArrayList<>();
-    explain(subs, stats, doc, freq.getValue().doubleValue(), docLen);
+    explain(subs, stats, freq.getValue().doubleValue(), docLen);
 
     return Explanation.match(
         (float) score(stats, freq.getValue().doubleValue(), docLen),
-        "score(" + getClass().getSimpleName() + ", doc=" + doc + ", freq=" +
+        "score(" + getClass().getSimpleName() + ", freq=" +
             freq.getValue() +"), computed as boost * " +
             "(term weight + document norm) from:",
         subs);

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/LMJelinekMercerSimilarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/LMJelinekMercerSimilarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/LMJelinekMercerSimilarity.java
index 42e5a7b..dde0650 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/LMJelinekMercerSimilarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/LMJelinekMercerSimilarity.java
@@ -74,7 +74,7 @@ public class LMJelinekMercerSimilarity extends LMSimilarity {
   }
 
   @Override
-  protected void explain(List<Explanation> subs, BasicStats stats, int doc,
+  protected void explain(List<Explanation> subs, BasicStats stats,
       double freq, double docLen) {
     if (stats.getBoost() != 1.0d) {
       subs.add(Explanation.match((float) stats.getBoost(), "boost"));
@@ -88,18 +88,18 @@ public class LMJelinekMercerSimilarity extends LMSimilarity {
         "freq, number of occurrences of term in the document");
     subs.add(explFreq);
     subs.add(Explanation.match((float) docLen,"dl, length of field"));
-    super.explain(subs, stats, doc, freq, docLen);
+    super.explain(subs, stats, freq, docLen);
   }
 
   @Override
   protected Explanation explain(
-      BasicStats stats, int doc, Explanation freq, double docLen) {
+      BasicStats stats, Explanation freq, double docLen) {
     List<Explanation> subs = new ArrayList<>();
-    explain(subs, stats, doc, freq.getValue().doubleValue(), docLen);
+    explain(subs, stats, freq.getValue().doubleValue(), docLen);
 
     return Explanation.match(
         (float) score(stats, freq.getValue().doubleValue(), docLen),
-        "score(" + getClass().getSimpleName() + ", doc=" + doc + ", freq=" +
+        "score(" + getClass().getSimpleName() + ", freq=" +
             freq.getValue() +"), computed as boost * " +
             "log(1 + ((1 - lambda) * freq / dl) /(lambda * P)) from:",
         subs);

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/LMSimilarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/LMSimilarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/LMSimilarity.java
index 8154806..73a1276 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/LMSimilarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/LMSimilarity.java
@@ -70,7 +70,7 @@ public abstract class LMSimilarity extends SimilarityBase {
   }
 
   @Override
-  protected void explain(List<Explanation> subExpls, BasicStats stats, int doc,
+  protected void explain(List<Explanation> subExpls, BasicStats stats,
       double freq, double docLen) {
     subExpls.add(Explanation.match((float) collectionModel.computeProbability(stats),
                                    "collection probability"));

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/MultiSimilarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/MultiSimilarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/MultiSimilarity.java
index 2f48cc6..3526db4 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/MultiSimilarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/MultiSimilarity.java
@@ -22,7 +22,6 @@ import java.util.ArrayList;
 import java.util.List;
 
 import org.apache.lucene.index.FieldInvertState;
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.CollectionStatistics;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.TermStatistics;
@@ -49,35 +48,27 @@ public class MultiSimilarity extends Similarity {
   }
 
   @Override
-  public SimWeight computeWeight(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
-    SimWeight subStats[] = new SimWeight[sims.length];
-    for (int i = 0; i < subStats.length; i++) {
-      subStats[i] = sims[i].computeWeight(boost, collectionStats, termStats);
-    }
-    return new MultiStats(subStats);
-  }
-
-  @Override
-  public SimScorer simScorer(SimWeight stats, LeafReaderContext context) throws IOException {
+  public SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
     SimScorer subScorers[] = new SimScorer[sims.length];
     for (int i = 0; i < subScorers.length; i++) {
-      subScorers[i] = sims[i].simScorer(((MultiStats)stats).subStats[i], context);
+      subScorers[i] = sims[i].scorer(boost, collectionStats, termStats);
     }
-    return new MultiSimScorer(subScorers);
+    return new MultiSimScorer(collectionStats.field(), subScorers);
   }
   
   static class MultiSimScorer extends SimScorer {
     private final SimScorer subScorers[];
     
-    MultiSimScorer(SimScorer subScorers[]) {
+    MultiSimScorer(String field, SimScorer subScorers[]) {
+      super(field);
       this.subScorers = subScorers;
     }
     
     @Override
-    public float score(int doc, float freq) throws IOException {
+    public float score(float freq, long norm) throws IOException {
       float sum = 0.0f;
       for (SimScorer subScorer : subScorers) {
-        sum += subScorer.score(doc, freq);
+        sum += subScorer.score(freq, norm);
       }
       return sum;
     }
@@ -92,21 +83,13 @@ public class MultiSimilarity extends Similarity {
     }
 
     @Override
-    public Explanation explain(int doc, Explanation freq) throws IOException {
+    public Explanation explain(Explanation freq, long norm) throws IOException {
       List<Explanation> subs = new ArrayList<>();
       for (SimScorer subScorer : subScorers) {
-        subs.add(subScorer.explain(doc, freq));
+        subs.add(subScorer.explain(freq, norm));
       }
-      return Explanation.match(score(doc, freq.getValue().floatValue()), "sum of:", subs);
+      return Explanation.match(score(freq.getValue().floatValue(), norm), "sum of:", subs);
     }
 
   }
-
-  static class MultiStats extends SimWeight {
-    final SimWeight subStats[];
-    
-    MultiStats(SimWeight subStats[]) {
-      this.subStats = subStats;
-    }
-  }
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/PerFieldSimilarityWrapper.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/PerFieldSimilarityWrapper.java b/lucene/core/src/java/org/apache/lucene/search/similarities/PerFieldSimilarityWrapper.java
index 6c05616..ee2381f 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/PerFieldSimilarityWrapper.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/PerFieldSimilarityWrapper.java
@@ -17,9 +17,6 @@
 package org.apache.lucene.search.similarities;
 
 
-import java.io.IOException;
-
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.FieldInvertState;
 import org.apache.lucene.search.CollectionStatistics;
 import org.apache.lucene.search.TermStatistics;
@@ -46,26 +43,13 @@ public abstract class PerFieldSimilarityWrapper extends Similarity {
   }
 
   @Override
-  public final SimWeight computeWeight(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
-    PerFieldSimWeight weight = new PerFieldSimWeight();
-    weight.delegate = get(collectionStats.field());
-    weight.delegateWeight = weight.delegate.computeWeight(boost, collectionStats, termStats);
-    return weight;
-  }
-
-  @Override
-  public final SimScorer simScorer(SimWeight weight, LeafReaderContext context) throws IOException {
-    PerFieldSimWeight perFieldWeight = (PerFieldSimWeight) weight;
-    return perFieldWeight.delegate.simScorer(perFieldWeight.delegateWeight, context);
+  public final SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
+    return get(collectionStats.field()).scorer(boost, collectionStats, termStats);
   }
   
   /** 
    * Returns a {@link Similarity} for scoring a field.
    */
   public abstract Similarity get(String name);
-  
-  static class PerFieldSimWeight extends SimWeight {
-    Similarity delegate;
-    SimWeight delegateWeight;
-  }
+
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/Similarity.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/Similarity.java b/lucene/core/src/java/org/apache/lucene/search/similarities/Similarity.java
index 5f0bcd0..a2ebe4a 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/Similarity.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/Similarity.java
@@ -19,16 +19,14 @@ package org.apache.lucene.search.similarities;
 
 import java.io.IOException;
 import java.util.Collections;
+import java.util.Objects;
 
+import org.apache.lucene.document.NumericDocValuesField;
 import org.apache.lucene.index.FieldInvertState;
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.CollectionStatistics;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.IndexSearcher;
-import org.apache.lucene.search.PhraseQuery;
-import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.search.TermStatistics;
-import org.apache.lucene.search.spans.SpanQuery;
 import org.apache.lucene.util.SmallFloat;
 
 /** 
@@ -38,9 +36,9 @@ import org.apache.lucene.util.SmallFloat;
  * <p>
  * This is a low-level API, you should only extend this API if you want to implement 
  * an information retrieval <i>model</i>.  If you are instead looking for a convenient way 
- * to alter Lucene's scoring, consider extending a higher-level implementation
- * such as {@link TFIDFSimilarity}, which implements the vector space model with this API, or 
- * just tweaking the default implementation: {@link BM25Similarity}.
+ * to alter Lucene's scoring, consider just tweaking the default implementation:
+ * {@link BM25Similarity} or extend {@link SimilarityBase}, which makes it easy to compute
+ * a score from index statistics.
  * <p>
  * Similarity determines how Lucene weights terms, and Lucene interacts with
  * this class at both <a href="#indextime">index-time</a> and 
@@ -49,23 +47,22 @@ import org.apache.lucene.util.SmallFloat;
  * <a name="indextime">Indexing Time</a>
  * At indexing time, the indexer calls {@link #computeNorm(FieldInvertState)}, allowing
  * the Similarity implementation to set a per-document value for the field that will 
- * be later accessible via {@link org.apache.lucene.index.LeafReader#getNormValues(String)}.  Lucene makes no assumption
- * about what is in this norm, but it is most useful for encoding length normalization 
- * information.
+ * be later accessible via {@link org.apache.lucene.index.LeafReader#getNormValues(String)}.
+ * Lucene makes no assumption about what is in this norm, but it is most useful for
+ * encoding length normalization information.
  * <p>
  * Implementations should carefully consider how the normalization is encoded: while
- * Lucene's {@link BM25Similarity} encodes a combination of index-time boost
- * and length normalization information with {@link SmallFloat} into a single byte, this 
- * might not be suitable for all purposes.
+ * Lucene's {@link BM25Similarity} encodes length normalization information with
+ * {@link SmallFloat} into a single byte, this might not be suitable for all purposes.
  * <p>
  * Many formulas require the use of average document length, which can be computed via a 
  * combination of {@link CollectionStatistics#sumTotalTermFreq()} and 
- * {@link CollectionStatistics#maxDoc()} or {@link CollectionStatistics#docCount()}, 
- * depending upon whether the average should reflect field sparsity.
+ * {@link CollectionStatistics#docCount()}.
  * <p>
- * Additional scoring factors can be stored in named
- * <code>NumericDocValuesField</code>s and accessed
- * at query-time with {@link org.apache.lucene.index.LeafReader#getNumericDocValues(String)}.
+ * Additional scoring factors can be stored in named {@link NumericDocValuesField}s and
+ * accessed at query-time with {@link org.apache.lucene.index.LeafReader#getNumericDocValues(String)}.
+ * However this should not be done in the {@link Similarity} but externally, for instance
+ * by using <tt>FunctionScoreQuery</tt>.
  * <p>
  * Finally, using index-time boosts (either via folding into the normalization byte or
  * via DocValues), is an inefficient way to boost the scores of different fields if the
@@ -76,14 +73,13 @@ import org.apache.lucene.util.SmallFloat;
  * <a name="querytime">Query time</a>
  * At query-time, Queries interact with the Similarity via these steps:
  * <ol>
- *   <li>The {@link #computeWeight(float, CollectionStatistics, TermStatistics...)} method is called a single time,
+ *   <li>The {@link #scorer(float, CollectionStatistics, TermStatistics...)} method is called a single time,
  *       allowing the implementation to compute any statistics (such as IDF, average document length, etc)
  *       across <i>the entire collection</i>. The {@link TermStatistics} and {@link CollectionStatistics} passed in 
  *       already contain all of the raw statistics involved, so a Similarity can freely use any combination
  *       of statistics without causing any additional I/O. Lucene makes no assumption about what is 
- *       stored in the returned {@link Similarity.SimWeight} object.
- *   <li>For each segment in the index, the Query creates a {@link #simScorer(SimWeight, org.apache.lucene.index.LeafReaderContext)}
- *       The score() method is called for each matching document.
+ *       stored in the returned {@link Similarity.SimScorer} object.
+ *   <li>Then {@link SimScorer#score(float, long)} is called for every matching document to compute its score.
  * </ol>
  * <p>
  * <a name="explaintime">Explanations</a>
@@ -126,37 +122,38 @@ public abstract class Similarity {
    * @param termStats term-level statistics, such as the document frequency of a term across the collection.
    * @return SimWeight object with the information this Similarity needs to score a query.
    */
-  public abstract SimWeight computeWeight(float boost,
+  public abstract SimScorer scorer(float boost,
       CollectionStatistics collectionStats, TermStatistics... termStats);
-
-  /**
-   * Creates a new {@link Similarity.SimScorer} to score matching documents from a segment of the inverted index.
-   * @param weight collection information from {@link #computeWeight(float, CollectionStatistics, TermStatistics...)}
-   * @param context segment of the inverted index to be scored.
-   * @return SloppySimScorer for scoring documents across <code>context</code>
-   * @throws IOException if there is a low-level I/O error
-   */
-  public abstract SimScorer simScorer(SimWeight weight, LeafReaderContext context) throws IOException;
   
-  /**
-   * API for scoring "sloppy" queries such as {@link TermQuery},
-   * {@link SpanQuery}, and {@link PhraseQuery}.
+  /** Stores the weight for a query across the indexed collection. This abstract
+   * implementation is empty; descendants of {@code Similarity} should
+   * subclass {@code SimWeight} and define the statistics they require in the
+   * subclass. Examples include idf, average field length, etc.
    */
   public static abstract class SimScorer {
-    
+
+    private final String field;
+
     /**
      * Sole constructor. (For invocation by subclass 
-     * constructors, typically implicit.)
+     * constructors.)
      */
-    public SimScorer() {}
+    public SimScorer(String field) {
+      this.field = Objects.requireNonNull(field);
+    }
+
+    /** Return the field that this {@link SimScorer} operates on. */
+    public final String getField() {
+      return field;
+    }
 
     /**
      * Score a single document
-     * @param doc document id within the inverted index segment
      * @param freq sloppy term frequency
+     * @param norm encoded normalization factor, as returned by {@link Similarity#computeNorm}, or {@code 1} if norms are disabled
      * @return document's score
      */
-    public abstract float score(int doc, float freq) throws IOException;
+    public abstract float score(float freq, long norm) throws IOException;
 
     /**
      * Return the maximum score that this scorer may produce for freqs in {@code ]0, maxFreq]}.
@@ -167,30 +164,16 @@ public abstract class Similarity {
 
     /**
      * Explain the score for a single document
-     * @param doc document id within the inverted index segment
      * @param freq Explanation of how the sloppy term frequency was computed
+     * @param norm encoded normalization factor, as returned by {@link Similarity#computeNorm}, or {@code 1} if norms are disabled
      * @return document's score
      */
-    public Explanation explain(int doc, Explanation freq) throws IOException {
+    public Explanation explain(Explanation freq, long norm) throws IOException {
       return Explanation.match(
-          score(doc, freq.getValue().floatValue()),
-          "score(doc=" + doc + ",freq=" + freq.getValue() +"), with freq of:",
+          score(freq.getValue().floatValue(), norm),
+          "score(freq=" + freq.getValue() +"), with freq of:",
           Collections.singleton(freq));
     }
-  }
-  
-  /** Stores the weight for a query across the indexed collection. This abstract
-   * implementation is empty; descendants of {@code Similarity} should
-   * subclass {@code SimWeight} and define the statistics they require in the
-   * subclass. Examples include idf, average field length, etc.
-   */
-  public static abstract class SimWeight {
-    
-    /**
-     * Sole constructor. (For invocation by subclass 
-     * constructors, typically implicit.)
-     */
-    public SimWeight() {}
 
   }
 }

http://git-wip-us.apache.org/repos/asf/lucene-solr/blob/8fd7ead9/lucene/core/src/java/org/apache/lucene/search/similarities/SimilarityBase.java
----------------------------------------------------------------------
diff --git a/lucene/core/src/java/org/apache/lucene/search/similarities/SimilarityBase.java b/lucene/core/src/java/org/apache/lucene/search/similarities/SimilarityBase.java
index f227f38..f750b12 100644
--- a/lucene/core/src/java/org/apache/lucene/search/similarities/SimilarityBase.java
+++ b/lucene/core/src/java/org/apache/lucene/search/similarities/SimilarityBase.java
@@ -22,8 +22,6 @@ import java.util.ArrayList;
 import java.util.List;
 
 import org.apache.lucene.index.FieldInvertState;
-import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.search.CollectionStatistics;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.TermStatistics;
@@ -33,7 +31,7 @@ import org.apache.lucene.util.SmallFloat;
  * A subclass of {@code Similarity} that provides a simplified API for its
  * descendants. Subclasses are only required to implement the {@link #score}
  * and {@link #toString()} methods. Implementing
- * {@link #explain(List, BasicStats, int, double, double)} is optional,
+ * {@link #explain(List, BasicStats, double, double)} is optional,
  * inasmuch as SimilarityBase already provides a basic explanation of the score
  * and the term frequency. However, implementers of a subclass are encouraged to
  * include as much detail about the scoring method as possible.
@@ -82,13 +80,18 @@ public abstract class SimilarityBase extends Similarity {
   }
   
   @Override
-  public final SimWeight computeWeight(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
-    BasicStats stats[] = new BasicStats[termStats.length];
+  public final SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
+    SimScorer weights[] = new SimScorer[termStats.length];
     for (int i = 0; i < termStats.length; i++) {
-      stats[i] = newStats(collectionStats.field(), boost);
-      fillBasicStats(stats[i], collectionStats, termStats[i]);
+      BasicStats stats = newStats(collectionStats.field(), boost);
+      fillBasicStats(stats, collectionStats, termStats[i]);
+      weights[i] = new BasicSimScorer(stats);
+    }
+    if (weights.length == 1) {
+      return weights[0];
+    } else {
+      return new MultiSimilarity.MultiSimScorer(collectionStats.field(), weights);
     }
-    return stats.length == 1 ? stats[0] : new MultiSimilarity.MultiStats(stats);
   }
   
   /** Factory method to return a custom stats object */
@@ -137,12 +140,11 @@ public abstract class SimilarityBase extends Similarity {
    * 
    * @param subExpls the list of details of the explanation to extend
    * @param stats the corpus level statistics.
-   * @param doc the document id.
    * @param freq the term frequency.
    * @param docLen the document length.
    */
   protected void explain(
-      List<Explanation> subExpls, BasicStats stats, int doc, double freq, double docLen) {}
+      List<Explanation> subExpls, BasicStats stats, double freq, double docLen) {}
   
   /**
    * Explains the score. The implementation here provides a basic explanation
@@ -151,43 +153,24 @@ public abstract class SimilarityBase extends Similarity {
    * attaches the score (computed via the {@link #score(BasicStats, double, double)}
    * method) and the explanation for the term frequency. Subclasses content with
    * this format may add additional details in
-   * {@link #explain(List, BasicStats, int, double, double)}.
+   * {@link #explain(List, BasicStats, double, double)}.
    *  
    * @param stats the corpus level statistics.
-   * @param doc the document id.
    * @param freq the term frequency and its explanation.
    * @param docLen the document length.
    * @return the explanation.
    */
   protected Explanation explain(
-      BasicStats stats, int doc, Explanation freq, double docLen) {
+      BasicStats stats, Explanation freq, double docLen) {
     List<Explanation> subs = new ArrayList<>();
-    explain(subs, stats, doc, freq.getValue().floatValue(), docLen);
+    explain(subs, stats, freq.getValue().floatValue(), docLen);
     
     return Explanation.match(
         (float) score(stats, freq.getValue().floatValue(), docLen),
-        "score(" + getClass().getSimpleName() + ", doc=" + doc + ", freq=" + freq.getValue() +"), computed from:",
+        "score(" + getClass().getSimpleName() + ", freq=" + freq.getValue() +"), computed from:",
         subs);
   }
   
-  @Override
-  public final SimScorer simScorer(SimWeight stats, LeafReaderContext context) throws IOException {
-    if (stats instanceof MultiSimilarity.MultiStats) {
-      // a multi term query (e.g. phrase). return the summation, 
-      // scoring almost as if it were boolean query
-      SimWeight subStats[] = ((MultiSimilarity.MultiStats) stats).subStats;
-      SimScorer subScorers[] = new SimScorer[subStats.length];
-      for (int i = 0; i < subScorers.length; i++) {
-        BasicStats basicstats = (BasicStats) subStats[i];
-        subScorers[i] = new BasicSimScorer(basicstats, context.reader().getNormValues(basicstats.field));
-      }
-      return new MultiSimilarity.MultiSimScorer(subScorers);
-    } else {
-      BasicStats basicstats = (BasicStats) stats;
-      return new BasicSimScorer(basicstats, context.reader().getNormValues(basicstats.field));
-    }
-  }
-  
   /**
    * Subclasses must override this method to return the name of the Similarity
    * and preferably the values of parameters (if any) as well.
@@ -227,33 +210,27 @@ public abstract class SimilarityBase extends Similarity {
   
   // --------------------------------- Classes ---------------------------------
   
-  /** Delegates the {@link #score(int, float)} and
-   * {@link #explain(int, Explanation)} methods to
+  /** Delegates the {@link #score(float, long)} and
+   * {@link #explain(Explanation, long)} methods to
    * {@link SimilarityBase#score(BasicStats, double, double)} and
-   * {@link SimilarityBase#explain(BasicStats, int, Explanation, double)},
+   * {@link SimilarityBase#explain(BasicStats, Explanation, double)},
    * respectively.
    */
   final class BasicSimScorer extends SimScorer {
-    private final BasicStats stats;
-    private final NumericDocValues norms;
+    final BasicStats stats;
     
-    BasicSimScorer(BasicStats stats, NumericDocValues norms) throws IOException {
+    BasicSimScorer(BasicStats stats) {
+      super(stats.field);
       this.stats = stats;
-      this.norms = norms;
     }
 
-    double getLengthValue(int doc) throws IOException {
-      if (norms == null) {
-        return 1D;
-      }
-      boolean found = norms.advanceExact(doc);
-      assert found;
-      return LENGTH_TABLE[Byte.toUnsignedInt((byte) norms.longValue())];
+    double getLengthValue(long norm) throws IOException {
+      return LENGTH_TABLE[Byte.toUnsignedInt((byte) norm)];
     }
     
     @Override
-    public float score(int doc, float freq) throws IOException {
-      return (float) SimilarityBase.this.score(stats, freq, getLengthValue(doc));
+    public float score(float freq, long norm) throws IOException {
+      return (float) SimilarityBase.this.score(stats, freq, getLengthValue(norm));
     }
 
     @Override
@@ -262,8 +239,8 @@ public abstract class SimilarityBase extends Similarity {
     }
 
     @Override
-    public Explanation explain(int doc, Explanation freq) throws IOException {
-      return SimilarityBase.this.explain(stats, doc, freq, getLengthValue(doc));
+    public Explanation explain(Explanation freq, long norm) throws IOException {
+      return SimilarityBase.this.explain(stats, freq, getLengthValue(norm));
     }
 
   }


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