Re: A85: Square roots

To: assembly-85@lists.ticalc.org
Subject: Re: A85: Square roots
From: Terry Peng <tpeng@geocities.com>
Date: Fri, 10 Oct 1997 16:52:24 -0500
References: <343E80CE.567D@hem2.passagen.se> <19971010.152247.8950.1.egillespie@juno.com>
Reply-To: assembly-85@lists.ticalc.org

Erik L Gillespie wrote:
> 
> I believe if you use Newton's method of finding roots you can do this
> easily
> 
> If you don't know Newton's method here it is:
>         Let X equal the number you want to find the square root of.
>         Let TOLERANCE be the accuracy of the root (1.0 * 10 ^ -7)
>         When programming, multiply by the inverse, don't divide (it's
> slow)
>         Multiply X by 0.5 and let this equal the current value of the
> root (call it ROOT)
>         Make a label here.
>         ROOT = (ROOT + (X / ROOT)) * 0.5
>         Put (ROOT * ROOT) - X in another spot for reference (call it
> TEMP)
>         Get absolute value of TEMP (if you don't know how ask me)
>         Compare TEMP and TOLERANCE
>         While TEMP > TOLERANCE continue jumping to your label.
>         Other wise you got your root
> 
> I'm definitely not the best at assembly but I can visualize how this
> would look, if you have any questions or corrections let me know.
> 
> Erik Huizing's method will work also but I'm sure this is much more
> efficient code and you won't have to calculate all the mod crap.  Besides
> this is Z-80 not BASIC

That's right... so how are you going to do X / ROOT ???
Assembly is not suited for decimals (you can write a routine, but it
gets tedious).
I think though that the original poster just wanted to find out if a
number was prime or not, so i think Erik's method would have worked just
fine. and btw mod is very easy:

;output: a=a%b
;usage: call &mod
;  or   CALL_(MOD)
mod:
	cp	b
	ret	c
	sub	b
	jr	mod

-- 
Terry Peng <tpeng@geocities.com>

References:

A85: Square roots

From: Max Thoursie <erdol@hem2.passagen.se>

Re: A85: Square roots

From: egillespie@juno.com (Erik L Gillespie)