fast arc tangent routine available?

[Yoshiaki Ohshima]

Hello, does anyone know if there are any 'arc tangent' routines, which run
faster than atan() and atan2() of the standard C math library?

I am now using Micro-Vax-II and (occasionally) PMAX, and have an impression
that my simple-minded table lookup using bisection search doesn't seem to
work well. Has anyone ever worked on this?

						--aki