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Atari coding BBS
| Re: CHK/CHK2 instructions |
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Posted by: Leonard
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May,11.2005-17:44
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I don't know that game code, but these intructions "may" be usefull for special ultra-optimisation :-) Explain:
In my fast mandelbrot routine, I use the instruction TRAPV. TRAPV flush an exeption if overflow flag is set. If not, it only takes 4 cyles. In a standard mandelbrot set, you have to check an exit condition at each iteration, and generally do 30 to 100 iterations before one and only exit. So using trapv takes only 4 cycles per iterations, instead of 8 for a BVS branch.
Anyway, I don't know the CHK timing instruction but it may be 4 cycles if CHK dn,dn exist. So in a loop where the exit condition does not occur very often ( say a 2d dot clipping routine), CHK may be usefull. ( again, IF it takes 4 cycles. If not, it's useless)
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