MPI_Request_c2f(3) on Linux
The text 7b5e54ee5521, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
Convert a request handle from its C representation to its Fortran representation