fast arc tangent routine availa

[mccaugh at s.cs.uiuc.edu]

 I really don't mean to sound pedantic (after all, if I did mean to, I would
 go over to the numerical-analysis group to do so) but I fail to see the
 virtue of speed for only a few decimal places: it doesn't seem terribly
 profound to cough up the first few terms of a Taylor Series, factoring the
 powers to exploit Horner's Rule and exclaim: "well, here is such a fast
 ArcTan series it doesn't require a loop!" I.e., yes it's fast--but at the
 expense of what? ACCURACY. (But for all that, it may be the fastest 3-place
 ArcTan routine available: for that, I commend the author!)

 Scott McCaughrin
 (mccaugh at s.cs.uiuc.edu)