should be it

external/duckdb/third_party/skiplist/SkipList.cpp

@@ -0,0 +1,40 @@
+//
+//  SkipList.cpp
+//  SkipList
+//
+//  Created by Paul Ross on 19/12/2015.
+//  Copyright (c) 2017 Paul Ross. All rights reserved.
+//
+
+#include <cstdlib>
+#ifdef SKIPLIST_THREAD_SUPPORT
+#include <mutex>
+#endif
+#include <string>
+
+#include "SkipList.h"
+
+namespace duckdb_skiplistlib {
+namespace skip_list {
+
+// This throws an IndexError when the index value >= size.
+// If possible the error will have an informative message.
+#ifdef INCLUDE_METHODS_THAT_USE_STREAMS
+void _throw_exceeds_size(size_t index) {
+    std::ostringstream oss;
+    oss << "Index out of range 0 <= index < " << index;
+    std::string err_msg = oss.str();
+#else
+void _throw_exceeds_size(size_t /* index */) {
+    std::string err_msg = "Index out of range.";
+#endif
+    throw IndexError(err_msg);
+}
+
+#ifdef SKIPLIST_THREAD_SUPPORT
+    std::mutex gSkipListMutex;
+#endif
+
+
+} // namespace SkipList
+} // namespace OrderedStructs