toms683, a FORTRAN77 code which evaluates an exponential integral with complex argument, by Donald Amos. This is a version of ACM TOMS algorithm 683.
The original version of toms683 is available through ACM: https://www.acm.org/pubs/calgo or NETLIB: https://www.netlib.org/toms/index.html
The computer code and data files made available on this web page are distributed under the MIT license
toms683 is available in a FORTRAN77 version.
Original Fortran77 version by Donald Amos.