Addchain: add comments on the code for ADDCHAIN_DBL
Addchain: add comments on the code for ADDCHAIN_DBL

mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs