Article View: comp.dsp
Article #1044Re: Looking for a fast exp(x) where -10.0<=x<=10.0
From: Ken Turkowski
Date: Fri, 02 Nov 1990 08:28
Date: Fri, 02 Nov 1990 08:28
24 lines
1471 bytes
1471 bytes
In a previous article, scott@walt.disney.com (Scott Watson) writes: >>Hi y'all - >> >>I have a need for an fast exp(x) function... >> >>x is a float and can range inside +-10.0. You can calculate exp(x) in fixed-point with a series of shifts and adds and a small lookup table using CORDIC iterations. Convergence is linear, so you get about one bit of precision with each iteration through a simple loop. With 32-bit words, you can probably get 26 bits of precision. If you can get by with less bits of precision, you can by with less iterations. I don't have the references handy, but I just recently published a paper in Graphics Gems (Academic Press, 1990) on CORDIC trigonometry. In the references to that paper are pointer to papers by Walthers and Chen which address exp, log, sqrt, and a host of other nonlinear functions. -- Ken Turkowski @ Apple Computer, Inc., Cupertino, CA Internet: turk@apple.com Applelink: TURK UUCP: sun!apple!turk
Technical Details
Message-ID:
<11086@goofy.Apple.COM>Path:
arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!turkReferences:
<1990Nov1.184820.5796@walt.disney.com> <16021@netcom.UUCP>Show Full Headers
Complete Article Headers
Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!turk From: turk@Apple.COM (Ken Turkowski) Newsgroups: comp.dsp,sci.math.num-analysis Subject: Re: Looking for a fast exp(x) where -10.0<=x<=10.0 Keywords: exp fast functions lookup tables Message-ID: <11086@goofy.Apple.COM> Date: 2 Nov 90 08:28:26 GMT References: <1990Nov1.184820.5796@walt.disney.com> <16021@netcom.UUCP> Organization: Advanced Technology Graphics, Apple Computer, Cupertino, CA, USA Lines: 24