Complex Exponential Integral

Hi Ethan,

In amos_airy.c, you write:

 * The cexint_() routine is also from the AMOS collection, but is not part
 * of the Bessel function subset and not included in libopenspecfun.
 * I could not find source for a version of the source that splits the
 * real and imaginary parts of the arguments as with the zxxxx.f Bessel
 * routines; this one accepts and returns a CMPLX argument rather than
separate
 * real and imaginary parts.
 *             D. E. Amos, ALGORITHM 683  A Portable FORTRAN Subroutine
 *             for Exponential Integrals of a Complex Argument
 *             ACM Trans. Math. Software 16:178-182 (1990)

This confuses me for two reasons:
- You invoke CEXINT as a double precision function, even though this
Fortran function is single precision.
- The algorithm 683 you quote DOES provide a separate double precision
function, ZEXINT. Moreover, that function does exactly what you were
looking for, namely taking and returning separate real and imaginary parts.

I changed f_amos_cexint to use ZEXINT (just for my own edification) and it
works properly. However, before submitting it, I wonder what am I missing?

Thank you,

Erik