Fast way to evaluate an exponential

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2 total messages Started by Ranjan S Muttiah Sun, 09 Jun 1991 07:12

#2021

Author: Ranjan S Muttiah
Date: Sun, 09 Jun 1991 07:12

4 lines
689 bytes

Is there a fast way to evaluate e^-x (using table look ups) than having to
use exp(.) in c ?  I have to call the exponential many times and looking for
ways to save time.

Re: Fast way to evaluate an exponential

#2022

Author: Jerry Penner
Date: Sun, 09 Jun 1991 08:26

13 lines
1146 bytes

In article <1991Jun9.071214.2073@noose.ecn.purdue.edu> muttiah@stable.ecn.purdue.edu (Ranjan S Muttiah) writes:
>
>Is there a fast way to evaluate e^-x (using table look ups) than having to
>use exp(.) in c ?  I have to call the exponential many times and looking for
>ways to save time.

Yes, use CORDIC algorithms.  These beasties usually use fixed point
arithmetic.  A recent issue of Dr. Dobbs Journal (hopefully available
at your library) gives a description and source code.  They don't use
table lookups but are fast.
-- 
Jerry Penner		  | jpenne@bode.ee.ualberta.ca
Edmonton, Alberta, Canada |  OR  alberta!bode!jpenne

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