1 files changed, 50 insertions, 10 deletions

diff --git a/core/string/ustring.cpp b/core/string/ustring.cpp
index 3d37e17ef8..c41ae1ccd8 100644
--- a/core/string/ustring.cpp
+++ b/core/string/ustring.cpp
@@ -1639,13 +1639,43 @@ Vector<int> String::split_ints_mk(const Vector<String> &p_splitters, bool p_allo
 }
 
 String String::join(const Vector<String> &parts) const {
+	if (parts.is_empty()) {
+		return String();
+	} else if (parts.size() == 1) {
+		return parts[0];
+	}
+
+	const int this_length = length();
+
+	int new_size = (parts.size() - 1) * this_length;
+	for (const String &part : parts) {
+		new_size += part.length();
+	}
+	new_size += 1;
+
 	String ret;
-	for (int i = 0; i < parts.size(); ++i) {
-		if (i > 0) {
-			ret += *this;
+	ret.resize(new_size);
+	char32_t *ret_ptrw = ret.ptrw();
+	const char32_t *this_ptr = ptr();
+
+	bool first = true;
+	for (const String &part : parts) {
+		if (first) {
+			first = false;
+		} else if (this_length) {
+			memcpy(ret_ptrw, this_ptr, this_length * sizeof(char32_t));
+			ret_ptrw += this_length;
+		}
+
+		const int part_length = part.length();
+		if (part_length) {
+			memcpy(ret_ptrw, part.ptr(), part_length * sizeof(char32_t));
+			ret_ptrw += part_length;
 		}
-		ret += parts[i];
 	}
+
+	*ret_ptrw = 0;
+
 	return ret;
 }
 
@@ -3149,7 +3179,7 @@ Vector<uint8_t> String::sha256_buffer() const {
 }
 
 String String::insert(int p_at_pos, const String &p_string) const {
-	if (p_at_pos < 0) {
+	if (p_string.is_empty() || p_at_pos < 0) {
 		return *this;
 	}
 
@@ -3157,17 +3187,27 @@ String String::insert(int p_at_pos, const String &p_string) const {
 		p_at_pos = length();
 	}
 
-	String pre;
+	String ret;
+	ret.resize(length() + p_string.length() + 1);
+	char32_t *ret_ptrw = ret.ptrw();
+	const char32_t *this_ptr = ptr();
+
 	if (p_at_pos > 0) {
-		pre = substr(0, p_at_pos);
+		memcpy(ret_ptrw, this_ptr, p_at_pos * sizeof(char32_t));
+		ret_ptrw += p_at_pos;
 	}
 
-	String post;
+	memcpy(ret_ptrw, p_string.ptr(), p_string.length() * sizeof(char32_t));
+	ret_ptrw += p_string.length();
+
 	if (p_at_pos < length()) {
-		post = substr(p_at_pos, length() - p_at_pos);
+		memcpy(ret_ptrw, this_ptr + p_at_pos, (length() - p_at_pos) * sizeof(char32_t));
+		ret_ptrw += length() - p_at_pos;
 	}
 
-	return pre + p_string + post;
+	*ret_ptrw = 0;
+
+	return ret;
 }
 
 String String::erase(int p_pos, int p_chars) const {