If your system lacks onexit() and you are not using an ANSI C compiler, then you should compile main.c with NO_ONEXIT defined. See the comments about onexit in the makefile. If your system has a double drem() function such that drem(a,b) is the IEEE remainder function (with double a, b), then you may wish to compile r_mod.c and d_mod.c with IEEE_drem defined. To check for transmission errors, issue the command make check This assumes you have the xsum program whose source, xsum.c, is distributed as part of "all from f2c/src". If you do not have xsum, you can obtain xsum.c by sending the following E-mail message to netlib@research.att.com send xsum.c from f2c/src