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From: gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>)
Newsgroups: net.lang.c
Subject: Re: C language hacking
Message-ID: <5823@brl-tgr.ARPA>
Date: Fri, 16-Nov-84 08:55:00 EST
Article-I.D.: brl-tgr.5823
Posted: Fri Nov 16 08:55:00 1984
Date-Received: Sat, 17-Nov-84 05:49:46 EST
References: <5715@brl-tgr.ARPA> <1161@orca.UUCP>
Organization: Ballistic Research Lab
Lines: 15

>> 	It would also be nice if sin( x ) and cos( x ) could be
>> 	computed simultaneously with reduced cost.  I doubt if this is
>> 	possible but would like to know if it is.

> 	sine = sin(x);
> 	cosine = sqrt(1.0 - sine*sine);

I wish people would check things out before posting them.  On our
4.2BSD system, the sqrt() approach is actually SLOWER than using
cos().  (Under UNIX System V it is very slightly faster.)  Now,
if I wanted cos(x)^2, I would certainly use 1 - sin(x)^2, which
I already knew about (I too went to high school).

What I had in mind was more along the lines of a CORDIC algorithm
or some other obscure but useful approach.