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Article #1064Re: Looking for a fast exp(x) where -10.0<=x<=10.0
From: Ken W. Sarkies
Date: Mon, 05 Nov 1990 03:56
Date: Mon, 05 Nov 1990 03:56
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1296 bytes
In article <1990Nov1.184820.5796@walt.disney.com> scott@walt.disney.com (Scott Watson) writes:
>
>I have a need for an fast exp(x) function...
>
Another idea I have used is the polynomial approximations as given in
Abramowitz and Stegun ``Handbook of Mathematical Functions''. For exp(x) you
can get accuracy to 2 x 10^{-10} for seven terms with 0<x<ln(2). Outside that
range use known results i.e. exp(x) = 2 x exp(x - ln(2)) for ln(2)<x<2ln(2).
The seven terms might be a bit much if you want real speed, but with other
suggestions given you may be able to tailor a useful algorithm depending on
your speed/accuracy/memory tradeoff.
--
Ken Sarkies
No disclaimer. My boss takes all responsibility for my big mouth.
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!munnari.oz.au!sirius.ucs.adelaide.edu.au!augean!ksarkies From: ksarkies@augean.ua.OZ.AU (Ken W. Sarkies) 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: <954@augean.ua.OZ.AU> Date: 5 Nov 90 03:56:23 GMT References: <1990Nov1.184820.5796@walt.disney.com> Organization: Engineering Faculty, University of Adelaide, Australia Lines: 17