From dd74869347e509c0b180c7ddfdeed392237838ea Mon Sep 17 00:00:00 2001
From: Adrien Grand <jpountz@gmail.com>
Date: Mon, 6 Jan 2020 09:02:51 +0100
Subject: [PATCH] BlockTreeTermsWriter should compute prefix lengths using
 Arrays#mismatch. (#1074)

---
 .../codecs/blocktree/BlockTreeTermsWriter.java     | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/lucene/core/src/java/org/apache/lucene/codecs/blocktree/BlockTreeTermsWriter.java b/lucene/core/src/java/org/apache/lucene/codecs/blocktree/BlockTreeTermsWriter.java
index dde6810af1d..deece0b5266 100644
--- a/lucene/core/src/java/org/apache/lucene/codecs/blocktree/BlockTreeTermsWriter.java
+++ b/lucene/core/src/java/org/apache/lucene/codecs/blocktree/BlockTreeTermsWriter.java
@@ -19,6 +19,7 @@ package org.apache.lucene.codecs.blocktree;
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 import org.apache.lucene.codecs.BlockTermState;
@@ -882,18 +883,17 @@ public final class BlockTreeTermsWriter extends FieldsConsumer {
 
     /** Pushes the new term to the top of the stack, and writes new blocks. */
     private void pushTerm(BytesRef text) throws IOException {
-      int limit = Math.min(lastTerm.length(), text.length);
-
       // Find common prefix between last term and current term:
-      int pos = 0;
-      while (pos < limit && lastTerm.byteAt(pos) == text.bytes[text.offset+pos]) {
-        pos++;
+      int prefixLength = Arrays.mismatch(lastTerm.bytes(), 0, lastTerm.length(), text.bytes, text.offset, text.offset + text.length);
+      if (prefixLength == -1) { // Only happens for the first term, if it is empty
+        assert lastTerm.length() == 0;
+        prefixLength = 0;
       }
 
       // if (DEBUG) System.out.println("  shared=" + pos + "  lastTerm.length=" + lastTerm.length);
 
       // Close the "abandoned" suffix now:
-      for(int i=lastTerm.length()-1;i>=pos;i--) {
+      for(int i=lastTerm.length()-1;i>=prefixLength;i--) {
 
         // How many items on top of the stack share the current suffix
         // we are closing:
@@ -910,7 +910,7 @@ public final class BlockTreeTermsWriter extends FieldsConsumer {
       }
 
       // Init new tail:
-      for(int i=pos;i<text.length;i++) {
+      for(int i=prefixLength;i<text.length;i++) {
         prefixStarts[i] = pending.size();
       }