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bogax
PostPosted: Wed Feb 23, 2011 4:08 am 
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Joined: Tue Nov 18, 2003 8:41 pm
Posts: 250
I have my own version but I'm pretty sure I've seen
better.

But I can't find them.

So I thought I'd ask if any one has or knows of a good
renedering of the algorithm in 6502 code?
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RichTW
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PostPosted: Wed Feb 23, 2011 8:00 am 
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Joined: Wed Oct 06, 2010 9:05 am
Posts: 95
Location: Palma, Spain
Look no further than this very website!
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bogax
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PostPosted: Wed Feb 23, 2011 9:03 am 
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Joined: Tue Nov 18, 2003 8:41 pm
Posts: 250
RichTW wrote:
Look no further than this very website!


I'm looking for something more akin to this

Code:
r=1
REPEAT
   x=x-r
   r=r+1
   x=x-r
UNTIL x<0
r=r-1


as mentioned here and other place by Garth Wilson

However, what I'm looking for uses the same basic idea but
goes about it a little differently IIRC
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RichTW
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PostPosted: Wed Feb 23, 2011 12:14 pm 
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Posts: 95
Location: Palma, Spain
Sorry, I misunderstood what you were asking! There's another implementation of it here, though I think this algorithm is probably a little suboptimal for square roots of large numbers (which have to iterate as many times as the result!).

The other algorithm always iterates exactly 8 times, and so it more-or-less time constant, regardless of the input.
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dclxvi
PostPosted: Thu Feb 24, 2011 2:20 am 
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Joined: Thu Mar 11, 2004 7:42 am
Posts: 362
bogax wrote:
I have my own version but I'm pretty sure I've seen
better.


I could've sworn I've seen one as well, but I can't remember where. Evidently, losing one's mind is contagious. :) Best I could come up on the spot is this (which subtracts 2r inside the loop instead of r twice):

Code:
   ldx #$FF
   sec
.1 inx
   inx
   stx tmp
   sbc tmp
   bcs .1
   txa
   lsr
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bogax
PostPosted: Thu Feb 24, 2011 4:26 am 
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Joined: Tue Nov 18, 2003 8:41 pm
Posts: 250
dclxvi wrote:
Best I could come up on the spot is this (which subtracts 2r inside the loop instead of r twice):

Code:
   ldx #$FF
   sec
.1 inx
   inx
   stx tmp
   sbc tmp
   bcs .1
   txa
   lsr


Cool! That's great. Thanks

Much better than mine, which seems like a kludgy mess.

Code:
 ldx #$00
LOOP
 sta num
 dex
 txa
 asl
 adc num
 bcs LOOP
 txa
 eor #$FF
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