[GitHub] [lucene] hendrikmuhs commented on a change in pull request #460: LUCENE-10247 - reduce size of FSTs by relative coding

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hendrikmuhs commented on a change in pull request #460:
URL: https://github.com/apache/lucene/pull/460#discussion_r754601969



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File path: lucene/core/src/java/org/apache/lucene/util/fst/FST.java
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@@ -1000,6 +1027,98 @@ private void writePresenceBits(
     assert bytePos - dest == numPresenceBytes;
   }
 
+  private long estimateNodeAddress(

Review comment:
       That's the trickiest part of the whole idea. I need to know [`thisNodeAddress`](https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/util/fst/FST.java#L779) before writing the state. But because everything uses variable length encodings, is based on flags, might write extra fields, etc. this is hard. I considered using the position of the arc, but, the compiler reverses the bytes it wrote.
   
   So what I ended up with is pre-calculating the node address ("estimate" is therefore wrong, feel free to suggest a better name, it must be exact (or return `0`, see below), so rather "preCalculateNodeAddress").
   
   Good to know: the heuristic is allowed to fail, in which case it returns `0` and relative coding isn't used.




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