From: Dave Tweed <pic@dtweed.com>
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Date: Sat, 12 Sep 2020 08:07:22 -0700
Subject: Re: [AVR] square on AVR
Thread-Topic: [AVR] square on AVR
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> I could use the last value as a starting value for the square root.
> Obviously the iron temperature won't be changing terribly fast, so
> that's a good suggestion.

Indeed, a single iteration of Newton-Raphson should be all you need.

In the case of square root, all you need to do is divide the current input
by the previous sqaure root, and then average that result with the previous
square root to get the new square root.

The "rule of thumb" with this method is that the number of correct bits
in the answer is basically doubled on each iteration. So as long as the
temperature hasn't changed enough to invalidate half of the bits in the
current answer, you're good to go.

Even at startup, when the "previous answer" is simply taken as some fixed
nonzero value (e.g., 2), this will converge within a few cycles to the
correct answer.

-- Dave Tweed
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