Xref: utzoo comp.lang.c:21326 comp.unix.questions:16035
Path: utzoo!utgpu!watmath!att!dptg!rutgers!iuvax!purdue!haven!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.lang.c,comp.unix.questions
Subject: Re: fast arc tangent routine available?
Keywords: math library, atan(), atan2(), arc tangent, table lookup
Message-ID: <10881@smoke.BRL.MIL>
Date: 30 Aug 89 21:42:56 GMT
References: <6002@pt.cs.cmu.edu>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 14

In article <6002@pt.cs.cmu.edu> aki@speech1.cs.cmu.edu (Yoshiaki Ohshima) writes:
>Hello, does anyone know if there are any 'arc tangent' routines, which run
>faster than atan() and atan2() of the standard C math library?

The library versions should be close to optimum.  The ones I know of are
pretty fast.

>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?

This is simply a numerical analysis question.  If you're not near 0, then
the atan curve is rather flat and a bisection search will not work well.
Why are you searching?