1984-12-17 11:03:13 +00:00
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.define Inn
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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 checks if a certain bit is set in a set
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! of n bytes on top of the stack.
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Inn:
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stx ARTH ! save bit number (lowbyte)
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sta ARTH+1 ! save bit number (highbyte)
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1988-08-19 17:05:03 +00:00
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and #0x80
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1984-12-17 11:03:13 +00:00
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beq 1f
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lda #0 ! bit number is negative
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sta ARTH+2 ! make it zero
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beq 3f
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1: txa
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1988-08-19 17:05:03 +00:00
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and #0x07 ! get bit number mod 8
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1984-12-17 11:03:13 +00:00
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tax
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lda #1
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cpx #0 ! bit number = 0
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beq 2f ! no shifting to right place
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1: asl a ! shift left until bit is in place
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dex
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bne 1b
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2: sta ARTH+2 ! bit is one in place
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ldx #3
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1: lsr ARTH+1 ! shift left 3 times bit number (highbyte)
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ror ARTH ! shift left 3 times bit number (lowbyte)
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dex ! this is bit number div 8
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bne 1b ! which is byte number
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3: lda SP+1
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ldx SP+2
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stx ADDR ! address of the set (lowbyte)
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sta ADDR+1 ! address of the set (highbyte)
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iny
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tya
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bne 2f
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inc SP+1
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2: clc ! remove the set
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adc SP+2
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sta SP+2 ! new stackpointer (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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ldy ARTH
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lda (ADDR),y ! load the byte in A
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bit ARTH+2 ! test bit
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bne 1f
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3: lda #0 ! bit is zero
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tax
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rts
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1: lda #0 ! bit is one
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ldx #1
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rts
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