Re: [Fractdev] Problems with Bignum sqrt()

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Author: Paul
Date:  
To: 'Fractint developer's list'
Subject: Re: [Fractdev] Problems with Bignum sqrt()
Hi Jonathan,

You're a genius :)

That fixed it.

Thanks a lot matie.

Paul.

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Paul de Leeuw Computers     NSW Central Coast, Australia
Email:                             pdeleeuw@???
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-----Original Message-----
From: fractdev-bounces@??? [mailto:fractdev-bounces@mailman.xmission.com] On Behalf Of Jonathan Osuch
Sent: Wednesday, 15 February 2012 12:53 PM
To: Fractint developer's list
Subject: Re: [Fractdev] Problems with Bignum sqrt()

Paul,

> I have been experimenting with converting all the Tierazon fractals to
> bignum. The only one I struggled with uses sqrt_bf(). I notice that
> this isn’t used anywhere in fractint, so I’m not sure if anyone has
> played with it.


Try replacing the division call:

unsafe_div_bf(bftmp3, n, r);

with:

div_bf(bftmp3, n, r);

The problem with using the unsafe version is that both n and r get modified by the call and we use r in the line that follows the division.

> I wrote a simple test program to check sqrt_bf() and it seemed to work
> okay for low precision numbers.


This is because our 'estimate' of the square root is the result of the function call to sqrtl(), which should give good results.

Jonathan




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