Re: [boost] [fixed_point] First presentation from GSoC 2015 and more

Subject: Re: [boost] [fixed_point] First presentation from GSoC 2015 and more
From: Michael Marcin (mike.marcin_at_[hidden])
Date: 2016-10-16 15:20:38

On 10/16/2016 12:52 PM, Christopher Kormanyos wrote:
>>> I would like to further investigate your sqrt implementation.
>
>> It seems the link to the whitepaper for sqrt has broken over the years.
>> I swear archive.org is the only thing keeping us from another dark age.
>
>> I found it again here:
>  OK. Thank you. I will try to bench the iterative sqrt algorithm for,let's say, 32-bit signed fixed-point on a 32-bit microcontroller.If I get any sensible results compared with our polynomialapproximation, I will forward them to the thread.
> One disadvantage of polynomial approximation is digit lossdue to argument reduction. Iterative and CORDIC seem tonot suffer from this, and cam be good options.
> Thanks for the suggestions.
>

Two things of note:
I'm pretty sure that sqrt is missing a bit of code to handle an odd 
number of fractional bits (I never used any types that had these but is 
probably important for a fully generic lib).

I'm pretty sure there is a low hanging fruit optimization opportunity to 
use CLZ to skip a bunch of iterations before starting the loop.