Calculating x^y, 2^x, etc.
If y is an integer, we can repeatedly multiply (or use even faster algorithms that repeatedly square and multiply).
If y is not an integer, we generally make the substitution
x^y = e^(y ln( x )) or x^y = 2^(y log2( x ))
and use some subroutine to calculate ln(x) and e^b -- or, alternatively, calculate log2(x) and 2^b.
(Is there a page somewhere on massmind describing logarithms and exponentials? Move the following text there.)
"Richard Feynman and The Connection Machine" by W. Daniel Hillis 1989 briefly describes Richard Feyman and the algorithm:
An Algorithm For Logarithms
Feynman worked out ... the subroutine for computing logarithms. I mention it here not only because it is a clever algorithm, but also because it is a specific contribution Richard made to the mainstream of computer science. He invented it at Los Alamos.
Consider the problem of finding the logarithm of a fractional number between 1.0 and 2.0 (the algorithm can be generalized without too much difficulty). Feynman observed that any such number can be uniquely represented as a product of numbers of the form 1 + 2-k, where k is an integer. Testing each of these factors in a binary number representation is simply a matter of a shift and a subtraction. Once the factors are determined, the logarithm can be computed by adding together the precomputed logarithms of the factors. The algorithm fit especially well on the Connection Machine.... The entire computation took less time than division.
Scott Dattalo has written a far more detailed explanation of Feynman's log2(x) algorithm, with worked-out examples .
|file: /Techref/microchip/math/power/index.htm, 4KB, , updated: 2007/5/16 22:40, local time: 2018/1/22 04:22,
|©2018 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.piclist.com/techref/microchip/math/power/index.htm"> PIC Microcontoller Basic Math Power Methods</A>
|Did you find what you needed?|
PICList 2018 contributors:
o List host: MIT, Site host massmind.org, Top posters @20180122 David C Brown, Isaac M. Bavaresco, Manu Abraham, RussellMc, Van Horn, David, Dwayne Reid, Harold Hallikainen, James Cameron, Sean Breheny, John Gardner,
* Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
Welcome to www.piclist.com!