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28 lines
532 B
ArmAsm
28 lines
532 B
ArmAsm
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; Piotr Fusik, 07.03.2018
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; originally by Ullrich von Bassewitz
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;
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; CC65 runtime: Decrement eax by value in Y
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;
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.export deceaxy
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.importzp sreg, tmp1
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deceaxy:
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sty tmp1
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sec
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sbc tmp1
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bcs @L9
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; borrow from X
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dex
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cpx #$ff
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bne @L9
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; X wrapped from zero to $ff, borrow from sreg
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dec sreg
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cpx sreg
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bne @L9
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; sreg wrapped from zero to $ff, borrow from sreg+1
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dec sreg+1
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@L9: rts
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