Performance optimization of SubstringSetMatcher::InsertPatternIntoAhoCorasickTree

extensions/common/matcher/substring_set_matcher.cc

Index: extensions/common/matcher/substring_set_matcher.cc
diff --git a/extensions/common/matcher/substring_set_matcher.cc b/extensions/common/matcher/substring_set_matcher.cc
index b5fdae6da37f80c3b9a1b963e1cbb052e54af8b5..27a950fb737c98dfb351825244ef7515b71a8b3b 100644
--- a/extensions/common/matcher/substring_set_matcher.cc
+++ b/extensions/common/matcher/substring_set_matcher.cc
@@ -101,26 +101,27 @@ void SubstringSetMatcher::RebuildAhoCorasickTree() {
 void SubstringSetMatcher::InsertPatternIntoAhoCorasickTree(
     const StringPattern* pattern) {
   const std::string& text = pattern->pattern();
-  size_t text_length = text.length();
+  const std::string::const_iterator text_end = text.end();
 
-  // Iterators on the tree and the text.
+  std::string::const_iterator text_iter = text.begin();
   int current_node = 0;
-  size_t text_pos = 0;
 
   // Follow existing paths for as long as possible.
-  while (text_pos < text_length &&
-         tree_[current_node].HasEdge(text[text_pos])) {
-    current_node = tree_[current_node].GetEdge(text[text_pos]);
-    ++text_pos;
+  int edge_to;
+  while (text_iter != text_end &&
+         (edge_to = tree_[current_node].GetEdge(*text_iter)) != -1) {
+    current_node = edge_to;
+    ++text_iter;
   }
 
   // Create new nodes if necessary.
-  while (text_pos < text_length) {
-    AhoCorasickNode new_node;
-    tree_.push_back(new_node);
-    tree_[current_node].SetEdge(text[text_pos], tree_.size() - 1);
-    current_node = tree_.size() - 1;
-    ++text_pos;
+  int new_node_position = tree_.size();
+  while (text_iter != text_end) {
+    tree_.push_back(AhoCorasickNode());
+    tree_[current_node].SetEdge(*text_iter, new_node_position);
+    current_node = new_node_position;
+    ++text_iter;
+    ++new_node_position;
   }
 
   // Register match.