QuickHull implementation by Antti Kuukka
Source: https://github.com/akuukka/quickhull

This implementation is 100% Public Domain.

The author's README states:

    This implementation is 100% Public Domain.

    Feel free to use.

The QuickHull source files themselves also carry the notice
"No copyrights. What follows is 100% Public Domain." in their header
comments.
