Re: A86: FindPixel in 84 cycles and 19 bytes!


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Re: A86: FindPixel in 84 cycles and 19 bytes!



On Fri, 8 Aug 1997 Dan Eble <eble@cis.ohio-state.edu> writes:

>On Fri, 8 Aug 1997 ariwsi@juno.com wrote:
>
>>  ; Here it is:  a FindPixel using only 84 clock cycles and 19 bytes!
>>  ; Call with H = Y coordinate, L = X coordinate
>
>The routine modifies the input registers, which would have to be pushed
>and popped, or reloaded, if this were to be called multiple times (which
>is highly likely).  This increases the number of clock cycles.

You shouldn't be calling it many times at all!  If using it in a sprite
plotting routine, it should only need to be called once!  After that,
you can just rotate the mask and increment the address when appropriate.
A sprite plotting routine would almost certainly use most of the
registers anyway, so you wouldn't have to push/pop any more than normal.
The only time that would be a problem is if you were using the FindPixel
routine for each pixel, which is a very bad idea!

(No, I don't really think there is much serious use for my routine,
but it is an entertaining idea!)

--
Patrick Davidson (ariwsi@juno.com)
Visit my home page!  Stuff for Amiga, TI-85, TI-92, even DOS!
http://www.calweb.com/~kwdavids/patrick/
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