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Subject: Re: Math in Rockbox

Re: Math in Rockbox

From: Andreas Stemmer <groovingandi_at_gmx.de>
Date: 2005-07-07

lear@algonet.se wrote:
> For an upcoming patch, I need some fixed- or floating-point math. Does
anyone have
> a good fixed-point implementation of pow(10, x) (or exp10(x)), or some
hints
> on how to implement it? It doesn't need to be particularly fast; small
size
> is to be preferred actually.

If x is an integer value, use one of the algorithms already given (lookup
table or while loop). If x can be fixed point as well, you could use some
kind of taylor approximation:

e^x = x^0/0! + x^1/1! + x^2/2! + x^3/3! + ...

with 10^x = (e^n)^x = e^(n*x)
and n = ln 10 = 2.302585093

for an implementation see
http://people.csail.mit.edu/hqm/imode/fplib/FP.java.html

Andreas
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Received on Thu Jul 7 08:35:39 2005


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