41 lines
780 B
ArmAsm
41 lines
780 B
ArmAsm
.define Set
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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 creates a set of n (n <= 256) bytes.
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! In this set a certain bit, which number is in registerpair AX,
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! is set. The rest is zero.
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Set:
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stx ARTH ! save bitnumber (lowbyte)
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sta ARTH+1 ! save bitnumber (highbyte)
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jsr Zer ! create n zerobytes
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lda ARTH
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and #07h ! n mod 8 (bitnumber in byte)
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tax
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lda #1
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cpx #0
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beq 2f
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1: asl a ! set bit (n mod 8)
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dex
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bne 1b
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2: sta ARTH+2
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ldx #3
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1: lsr ARTH+1 ! shiftright n 3 times (= n div 8)
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ror ARTH ! this is the bytenumber
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dex
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bne 1b
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ldy ARTH ! load bytenumber
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lda SP+1
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ldx SP+2
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stx ADDR ! address of set (lowbyte)
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sta ADDR+1 ! address of set (highbyte)
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lda ARTH+2 ! get bit
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sta (ADDR),y ! store byte with bit on
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rts
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