[GitHub] [lucene-solr] rmuir commented on a change in pull request #2457: LUCENE-9824: Hunspell suggestions: speed up ngram score calculation for each dictionary entry

[GitBox <gi...@apache.org>]

rmuir commented on a change in pull request #2457:
URL: https://github.com/apache/lucene-solr/pull/2457#discussion_r588280433



##########
File path: lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/TrigramAutomaton.java
##########
@@ -0,0 +1,122 @@
+/*
+ * 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.analysis.hunspell;
+
+import java.util.HashMap;
+import java.util.Map;
+import org.apache.lucene.util.FixedBitSet;
+import org.apache.lucene.util.automaton.Automaton;
+import org.apache.lucene.util.automaton.CharacterRunAutomaton;
+import org.apache.lucene.util.automaton.Operations;
+
+/**
+ * An automaton allowing to achieve the same results as non-weighted {@link
+ * GeneratingSuggester#ngramScore}, but faster (in O(s2.length) time).
+ */
+class TrigramAutomaton {
+  private static final int N = 3;
+  private final CharacterRunAutomaton automaton;
+  private final int[] state2Score;
+  private final FixedBitSet countedSubstrings;
+
+  TrigramAutomaton(String s1) {
+    Map<String, Integer> substringCounts = new HashMap<>();
+
+    Automaton.Builder builder = new Automaton.Builder(s1.length() * N, s1.length() * N);
+    int initialState = builder.createState();
+
+    for (int start = 0; start < s1.length(); start++) {
+      int limit = Math.min(s1.length(), start + N);
+      for (int end = start + 1; end <= limit; end++) {
+        substringCounts.merge(s1.substring(start, end), 1, Integer::sum);
+      }
+
+      int state = initialState;
+      for (int i = start; i < limit; i++) {
+        int next = builder.createState();
+        builder.addTransition(state, next, s1.charAt(i));
+        state = next;
+      }
+    }
+
+    automaton =
+        new CharacterRunAutomaton(

Review comment:
       just curious, did you try this algorithm without tableizing Automaton into RunAutomaton? The RunAutomaton has some initial construction costs... at some point when you run enough strings through it, that investment pays off and was worth your time. But I don't know the numbers here and whether or not it is worth it




----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org



---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscribe@lucene.apache.org
For additional commands, e-mail: issues-help@lucene.apache.org