> I don't know if there is an open source implementation

If you mean OpenCL, then yes, there is one under development:

http://www.phoronix.com/scan.php?page=news_item&px=MTEwMjU
http://tstellar.blogspot.com/2012/03/how-to-test-clover-with-r600g.html (for R800/R900)
http://www.x.org/wiki/XorgEVoC/GalliumCompute (for nVidia)
https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=7853&forum=3&start=1