Path: utzoo!attcan!uunet!tank!ncar!asuvax!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!ucsd!nosc!spectra!bseeg
From: bseeg@spectra.COM (Bob Seegmiller)
Newsgroups: comp.graphics
Subject: Inverse Square Root Algorithm Request
Summary: Request for 1/sqrt(x) algorithm
Keywords: Square Root,Numerical Methods,Algorithms,SIGGRAPH
Message-ID: <325@spectra.COM>
Date: 8 Feb 90 01:41:26 GMT
Reply-To: bseeg@spectra (Bob Seegmiller)
Distribution: comp.graphics,comp.misc
Organization: Spectragraphics, Corp., San Diego, CA
Lines: 9

At the '86 SIGGRAPH Conference, in the Image Rendering class or at one
of the Forums, Rob Cook of Pixar gave passing mention of a method for
computing the inverse square root (n^-(.5)) of a number that was
faster(!?) or comparable in speed to taking just the square root
itself.  I've lost the note, and my own hack at it via Newton's method
has proved to be highly unstable.  Does anyone out there know of or
remember the reference?

Thanks in advance.