Subject: [stella] Usefull illegal opcodes (part 1) From: "Thomas Jentzsch" <tjentzsch@xxxxxx> Date: Fri, 23 Feb 2001 08:59:28 +0100 |
Hi, yesterday, i was thinking about a faster way to decide in a kernel if you are on a sprite drawing line or not. The best way, i knew until now, was (if y contains linecounter): tya ; 2 (sec ; 2) <- this can sometimes be avoided sbc SpriteEnd ; 3 adc #SPRITEHEIGHT ; 2 bcx .skipDraw ; 2 = 9-11 cycles ... If you like using illegal opcodes, you can use dcp (dec,cmp) here: lda #SPRITEHEIGHT ; 2 dcp SpriteEnd ; 5 initial value has to be adjusted bcx .skipDraw ; 2 = 9 ... Advantages: - state of carry flag doesn't matter anymore (may save 2 cycles) - a remains constant, could be useful for a 2nd sprite - you could use the content of SpriteEnd instead of y for accesing sprite data - ??? Have fun! Thomas _______________________________________________________ Thomas Jentzsch | *** Every bit is sacred ! *** tjentzsch at web dot de | _______________________________________________________________________ 1.000.000 DM gewinnen - kostenlos tippen - http://millionenklick.web.de IhrName@xxxxxx, 8MB Speicher, Verschluesselung - http://freemail.web.de - Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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