-----Original Message-----
From: Russell McMahon [mailto:apptech@PARADISE.NET.NZ]
Sent: 03 October 2003 05:18
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [pic]: square roots for the 18F

FWIW, and you all may have better ways of doing this, square root can be
used directly to build a log function using otherwise only shift and add. It
may be that this information is more useful to people with a 4 function plus
sqrt calculators who want a log function :-)

eg using said calculator

    log10(X) ~= (sqrt.sqrt.sqrt.sqrt.sqrt.sqrt.sqrt.sqrt.(X) - 1 ) x 889

As you change the number of sqrts only the constant changes to get the right
answer (subject to accuracy constraints)

If this looks obscure try geting the answer for log2 with various sqrts and
changing the constant.
(Hint: Constant looks suyspiciously like 2^N )



Couldn't get this to work e.g.:

LOG10(20) = 1.301

20 ('square rooted' 8 times) = 1.0117

(1.0117 - 1) * 889 = 10.46

What am I doing wrong?  I suspect I am interpreting the sqrt.sqrt.sqrt etc.
operation wrongly.

Mike




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