MPI_Cart_coords(3) on Linux
The text 17cdd9fde71e, as Debian 13 (Trixie), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy) shipped it.
Determines process coords in cartesian topology given rank in group