Optimizing remove_whitespace performance

solomonwzs · tordex · commit 171e03d7acce · 2025-04-02T17:11:55.000+03:00
fix #397
diff --git a/src/css_parser.cpp b/src/css_parser.cpp
@@ -38,7 +38,48 @@ void filter_code_points(string& input)
 	input = result;
 }
 
-void remove_whitespace(css_token_vector& tokens, keep_whitespace_fn keep_whitespace)
+static const size_t kLargeSize = 50;
+static void remove_whitespace_large(css_token_vector& tokens, keep_whitespace_fn keep_whitespace);
+static void remove_whitespace_small(css_token_vector& tokens, keep_whitespace_fn keep_whitespace);
+
+void remove_whitespace_large(css_token_vector& tokens, keep_whitespace_fn keep_whitespace)
+{
+	std::vector<int> keep_idx;
+	keep_idx.reserve(tokens.size());
+	for (int i = 0; i < static_cast<int>(tokens.size()); ++i)
+	{
+		auto &tok = tokens[i];
+		bool keep = true;
+		if (tok.type == ' ')
+		{
+			const auto &left = i > 0 ? tokens[i - 1] : css_token();
+			const auto &right = at(tokens, i + 1);
+			keep = keep_whitespace && keep_whitespace(left, right);
+		}
+		else if (tok.is_component_value())
+		{
+			if (tok.value.size() > kLargeSize)
+				remove_whitespace_large(tok.value, keep_whitespace);
+			else
+				remove_whitespace_small(tok.value, keep_whitespace);
+		}
+		if (keep)
+			keep_idx.push_back(i);
+	}
+
+	if (keep_idx.size() == tokens.size())
+		return;
+	else
+	{
+		css_token_vector tmp;
+		tmp.reserve(keep_idx.size());
+		for (auto idx : keep_idx)
+			tmp.push_back(tokens[idx]);
+		tokens.swap(tmp);
+	}
+}
+
+void remove_whitespace_small(css_token_vector& tokens, keep_whitespace_fn keep_whitespace)
 {
 	for (int i = 0; i < (int)tokens.size(); i++)
 	{
@@ -48,13 +89,27 @@ void remove_whitespace(css_token_vector& tokens, keep_whitespace_fn keep_whitesp
 			const auto& left = i > 0 ? tokens[i - 1] : css_token();
 			const auto& right = at(tokens, i + 1);
 			bool keep = keep_whitespace && keep_whitespace(left, right);
-			if (!keep) remove(tokens, i), i--;
+			if (!keep)
+				remove(tokens, i), i--;
 		}
 		else if (tok.is_component_value())
-			remove_whitespace(tok.value, keep_whitespace);
+		{
+			if (tok.value.size() > kLargeSize)
+				remove_whitespace_large(tok.value, keep_whitespace);
+			else
+				remove_whitespace_small(tok.value, keep_whitespace);
+		}
 	}
 }
 
+void remove_whitespace(css_token_vector& tokens, keep_whitespace_fn keep_whitespace)
+{
+	if (tokens.size() > kLargeSize)
+		remove_whitespace_large(tokens, keep_whitespace);
+	else
+		remove_whitespace_small(tokens, keep_whitespace);
+}
+
 void componentize(css_token_vector& tokens)
 {
 	css_parser parser(tokens);
@@ -511,4 +566,4 @@ bool skip_whitespace(const css_token_vector& tokens, int& index)
 	return index != start;
 }
 
-} // namespace litehtml
+} // namespace litehtml
