1984-12-17 11:03:13 +00:00
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.define Exg
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1987-01-30 18:41:42 +00:00
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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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1984-12-17 11:03:13 +00:00
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! This subroutine exchanges two groups of bytes on the top of the
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! stack. The groups may consist of atmost 255 bytes.
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! This number is in register Y.
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! The exchange is from ADDR, ADDR+1 to ADDR+2, ADDR+3
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Exg:
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lda SP+1
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ldx SP+2
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stx ADDR ! address of first group (lowbyte)
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sta ADDR+1 ! address of first group (highbyte)
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sty Ytmp ! save number of bytes to be exchanged
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clc
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lda SP+2
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adc Ytmp
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sta ADDR+2 ! address of second group (lowbyte)
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lda SP+1
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adc #0
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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 from first group
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pha ! temporary save
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lda (ADDR+2),y ! get byte from second group
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sta (ADDR),y ! store in first group
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pla ! get temporary saved byte
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sta (ADDR+2),y ! store in second group
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tya
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bne 1b ! perform n times
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rts
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