ephemeris program sought

[edl%sri-tsc at sri-unix.UUCP]

I'm looking for a program or algorithm for generating a planetary
ephemeris.  It need only be accurate to about 30 seconds and good for
this and the next century. Ideally it would run under UNIX or CP/M
and be written in C but at this point I'd like to see the source for
whatever exists. 
Any suggestions or pointer would be greatly appreciated.
Thanks.

Jan Edl
edl at sri-tsc