MPI_File_get_type_extent(3) on Linux
The text 0e1c8733bbe7, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy) shipped it.
Returns the extent of datatype in the file