Implement istring::insert with given index and count

src/string.cpp

@@ -205,7 +205,33 @@ istring& istring::insert(size_t index, const istring& str) {
 
 	// only copy the string if there is room
 	size_t num_to_copy = std::min(str.m_size, space);
-	mtl::memmove(substr, str.m_str, num_to_copy);
+	mtl::memcpy(substr, str.m_str, num_to_copy);
+
+	m_size += num_to_copy;
+	m_str[m_size] = '\0';
+	
+	return *this;
+}
+
+istring& istring::insert(size_t index, const istring& str, size_t str_index, size_t count) {
+	if (count == npos) {
+		count = str.m_size - str_index;
+	}
+
+	char* substr = m_str + index;
+	size_t space = m_capacity - index;
+
+	if (space > count) {
+		size_t space_to_move = space - count;
+		size_t items_to_move = m_size - index;
+		// only move items if there is room, and they exist
+		size_t num_to_move = std::min(items_to_move, space_to_move);
+		mtl::memmove(substr + count, substr, num_to_move);
+	}
+
+	// only copy the string if there is room
+	size_t num_to_copy = std::min(count, space);
+	mtl::memcpy(substr, str.m_str + str_index, num_to_copy);
 
 	m_size += num_to_copy;
 	m_str[m_size] = '\0';