This implementations might be useful if you are playing around with Microchip Keeloq chips.
I verified that this algorithm gives the same results as that produced by the Microchip SDK for several test cases.
The Keeloq algorithm is not patented.
However, since Microchip does hold a patent on its application to secure keyless entry,
it probably would not be wise to make a commercial secure keyless entry product using this algorithm in a non-Microchip processor.
Personal experimentation should be okay.
If you decide to make something commercial, buy Microchip's processors.