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From: falk@peregrine.Sun.COM (Ed Falk)
Newsgroups: comp.graphics
Subject: Re: 2 3D Vectors: Get a 3rd perp. to 1st? (Also, renorm. matrices)
Message-ID: <6251@exodus.Eng.Sun.COM>
Date: 18 Jan 91 19:16:21 GMT
References: <6613@crash.cts.com> <22365@well.sf.ca.us> <6660@crash.cts.com> <1991Jan15.233218.7646@watdragon.waterloo.edu> <7012@crash.cts.com>
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Organization: Sun Microsystems, Mt. View, Ca.
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In article <7012@crash.cts.com> jcs@crash.cts.com (John Schultz) writes:
>In <1991Jan15.233218.7646@watdragon.waterloo.edu> ccplumb@rose.uwaterloo.ca (Colin Plumb) writes:
>
>  Yuck! First, I do two table lookups because I have sin and asin tabled
>already for all possible cases. Can't do that for sqrt...

Sure you can.  Just have a table of all your sqrts from sqrt(1) to
sqrt(4) at any resolution you want.  Then:

	i = 0 ;
	while(x < 1.)
	  x *= 4. , ++i ;
	while(x > 4.)
	  x *= .25 , --i ;
	x = sqrt_table_lookup(x) ;
	while( i > 0 )
	  x *= .5 ;
	while( i < 0 )
	  x *= 2. ;


(Optimization left as an excercise to the student.  A smart compiler
should be able to convert the multiplies into increments or decrements
of the exponent.)

		-ed falk, sun microsystems
		 sun!falk, falk@sun.com
To be loyal to rags, to shout for rags, to worship rags, to die for rags 
-- that is a loyalty of unreason, it is pure animal (Mark Twain).