I believe the emacs implementation is due to Reingold and Dershowitz[1] On page 11 of this pdf they give quite a bit of detail about the calculation of French R

I believe the emacs implementation is due to Reingold and Dershowitz[1] On page 11 of this pdf they give quite a bit of detail about the calculation of French Revolutionary Calendar, (including leap year complications). [1] http://www.reingold.co/cc2-paper.pdf http://www.reingold.co/cc2-paper.pdf