35 lines
710 B
ArmAsm
35 lines
710 B
ArmAsm
.define Xor
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.sect .text
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.sect .rom
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.sect .data
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.sect .bss
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.sect .text
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! This subroutine performs the exclusive or on two groups of bytes.
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! The groups consists of atmost 254 bytes.
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! The result is on top of the stack.
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Xor:
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lda SP+1
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sta ADDR+1 ! address of first group (lowbyte)
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lda SP+2
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sta ADDR ! address of first group (highbyte)
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clc
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tya
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adc SP+2
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sta SP+2 ! new stackpointer (lowbyte)
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sta ADDR+2 ! address of second group (lowbyte)
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lda #0
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adc SP+1
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sta SP+1 ! new stackpointer (highbyte)
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sta ADDR+3 ! address of second group (highbyte)
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1: dey
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lda (ADDR),y ! get byte first group
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eor (ADDR+2),y ! exclusive or with byte second group
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sta (ADDR+2),y ! restore result
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tya
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bne 1b
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rts
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