35 lines
666 B
ArmAsm
35 lines
666 B
ArmAsm
.define Dup
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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 duplicate's the top n (in register Y) bytes.
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! N is atmost 256.
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! The duplicating takes place as follows.
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! The registerpair is filled with the bytes at stackpointer + N
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! and stackpopinter + N-1.
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! These two bytes then are pushed onto the stack.
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! Next the offset N is decremented and the next two byte are taken
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! care off. Until N = 0.
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Dup:
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lda SP+1
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ldx SP+2
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stx ADDR ! address of group (lowbyte)
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sta ADDR+1 ! address of group (highbyte)
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1: dey
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lda (ADDR),y ! get lowbyte
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pha
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dey
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lda (ADDR),y ! get highbyte
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tax
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pla
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jsr Push ! push them
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tya
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bne 1b
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rts
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