ca65 V2.17 - Git 582aa41
Main file   : 8queens.ca65
Current file: 8queens.ca65

000000r 1               ;
000000r 1               ; ACORN System 1 Applications: Eight Queen's Problem
000000r 1               ;
000000r 1               ; From the Acorn System 1 User's Manual
000000r 1               ;
000000r 1               ; (Chris Oddy January 2022)
000000r 1               ;
000000r 1               ; entry point $0200
000000r 1               ;
000000r 1               		.setcpu			"6502"
000000r 1               		.listbytes		unlimited
000000r 1               ;
000000r 1               COUNT	:=		$19
000000r 1               ROW		:=		$20
000000r 1               LEFT	:=		$29
000000r 1               RIGHT	:=		$32
000000r 1               RDHEXTD	:=		$FE60		; right double hex to display
000000r 1               RESTART	:=		$FF04		; monitor reentry point
000000r 1               ;
000000r 1               		.org			$0200
000200  1               ;
000200  1  F8           QUEENS:	sed
000201  1  A2 20        		ldx		#$20
000203  1  84 19        		sty		COUNT		; clear count
000205  1  84 20        		sty		ROW			; clear row occupied
000207  1  84 29        		sty		LEFT		; clear left diagonal attacks
000209  1  84 32        		sty		RIGHT		; clear right diagonal attacks
00020B  1  20 16 02     		jsr		TRY			; find the No. of ways
00020E  1  A5 19        		lda		COUNT
000210  1  20 60 FE     		jsr		RDHEXTD		; display answer
000213  1  4C 04 FF     		jmp		RESTART
000216  1  B5 00        TRY:	lda		$00,x		; finished yet ?
000218  1  C9 FF        		cmp		#$FF
00021A  1  D0 07        		bne		CONTIN
00021C  1  A5 19        		lda		COUNT		; finished, so increment count
00021E  1  69 00        		adc		#$00
000220  1  85 19        		sta		COUNT
000222  1  60           FINISH:	rts
000223  1  15 09        CONTIN:	ora		$09,x		; current left
000225  1  15 12        		ora		$12,x		; current right
000227  1  A8           LOOP:	tay
000228  1  49 FF        		eor		#$FF
00022A  1  F0 F6        		beq		FINISH		; no chance
00022C  1  95 1B        		sta		$1B,x		; current possible place
00022E  1  C8           		iny
00022F  1  98           		tya
000230  1  35 1B        		and		$1B,x
000232  1  A8           		tay
000233  1  15 00        		ora		$00,x
000235  1  95 01        		sta		$01,x		; new row
000237  1  98           		tya
000238  1  15 09        		ora		$09,x
00023A  1  0A           		asl		A
00023B  1  95 0A        		sta		$0A,x		; new left attack
00023D  1  98           		tya
00023E  1  15 12        		ora		$12,x
000240  1  4A           		lsr		A
000241  1  95 13        		sta		$13,x		; new right attack
000243  1  E8           		inx
000244  1  20 16 02     		jsr		TRY
000247  1  CA           		dex
000248  1  B5 01        		lda		$01,x
00024A  1  49 FF        		eor		#$FF
00024C  1  35 1B        		and		$1B,x
00024E  1  49 FF        		eor		#$FF
000250  1  4C 27 02     		jmp		LOOP
000250  1