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22 lines
479 B
Plaintext
22 lines
479 B
Plaintext
PT3_player
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ASR = CMP #$80 / ROR
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Notes:
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signed 8-bit comparison
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see http://6502.org/tutorials/compare_beyond.html#2.2
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SEC ; prepare carry for SBC
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SBC NUM ; A-NUM
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BVC LABEL ; if V is 0, N eor V = N, otherwise N eor V = N eor 1
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EOR #$80 ; A = A eor $80, and N = N eor 1
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LABEL
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If the N flag is 1, then A (signed) < NUM (signed) and BMI will branch
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If the N flag is 0, then A (signed) >= NUM (signed) and BPL will branch
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