28 lines
583 B
ArmAsm
28 lines
583 B
ArmAsm
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.define Addsub
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! This subroutine is used by the fourbyte addition and subtraction
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! routines.
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! It puts the address of the second operand into
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! the zeropage locations ADDR and ADDR+1
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! The address of the first operand is put into
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! zeropage locations ADDR+2 and ADDR+3.
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Addsub:
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clc
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lda SP+2
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sta ADDR ! address of second operand (lowbyte)
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adc #4
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sta SP+2
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sta ADDR+2 ! address of first operand (lowbyte)
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lda SP+1
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sta ADDR+1 ! address of second operand (highbyte)
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adc #0
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sta ADDR+3 ! address of first operand (highbyte)
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sta SP+1
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ldy #0
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ldx #0FCh ! do it 4 times
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rts
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