Spilornis is part of the Eagle project.
It is an optional utility library that implements the Tcl list splitting and joining algorithm in native code.
When enabled, it is used by the core Eagle library (i.e. managed code) to improve processing speed.
It is fully Unicode (UCS-2 / UTF-16) aware, is based on the official Tcl sources, and may be used by any project.
The source code can be seen at Eagle Native Utility Library (Spilornis)