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

000000r 1               ;
000000r 1               ; ACORN System 1 Applications: Divider
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 for decimal and $0203 for hexadecimal
000000r 1               ;
000000r 1               		.setcpu			"6502"
000000r 1               		.listbytes		unlimited
000000r 1               ;
000000r 1               DIVIDR	:=		$20
000000r 1               DIVISR	:=		$22
000000r 1               RESULT	:=		$24
000000r 1               RESTART	:=		$FF04		; Monitor renentry point
000000r 1               RDHEXTD	:=		$FE60		; write double hex to display
000000r 1               QHEXTD1	:=		$FE64		; quad hex to display 1
000000r 1               QDATFET	:=		$FE88		; quad data fetch
000000r 1               ;
000000r 1               		.org			$0200
000200  1               ;
000200  1  F8           DIVDEC:	sed					; entry point for decimal divide
000201  1  F0 01        		beq		DIVIDE		; always branch
000203  1  D8           DIVHEX:	cld					; entry point for hexadecimal divide
000204  1  84 20        DIVIDE:	sty		DIVIDR		; clear dividend - prompt for number
000206  1  84 21        		sty		DIVIDR+1
000208  1  A9 11        		lda		#$11		; prompt for second number
00020A  1  85 22        		sta		DIVISR
00020C  1  A2 20        		ldx		#$20
00020E  1  20 88 FE     		jsr		QDATFET		; fetch dividend
000211  1  A2 22        		ldx		#$22
000213  1  20 88 FE     		jsr		QDATFET		; fetch divisor
000216  1  84 24        		sty		RESULT		; clear result
000218  1  84 25        		sty		RESULT+1
00021A  1  A4 20        		ldy		DIVIDR		; use Y & X as double accumulator
00021C  1  A6 21        		ldx		DIVIDR+1
00021E  1  38           SUB:	sec					; subtract the divisor
00021F  1  98           		tya
000220  1  E5 22        		sbc		DIVISR
000222  1  A8           		tay
000223  1  8A           		txa
000224  1  E9 00        		sbc		#$00
000226  1  AA           		tax
000227  1  90 10        		bcc		RESLT		; if negative then finished
000229  1  84 23        		sty		DIVISR+1	; else update the remainder
00022B  1  A5 24        		lda		RESULT		; and add one to the result
00022D  1  69 00        		adc		#$00		; (carry was set on input)
00022F  1  85 24        		sta		RESULT
000231  1  A5 25        		lda		RESULT+1
000233  1  69 00        		adc		#$00
000235  1  85 25        		sta		RESULT+1
000237  1  90 E5        		bcc		SUB			; no carry is possible (usually)
000239  1  A2 24        RESLT:	ldx		#$24
00023B  1  20 64 FE     		jsr		QHEXTD1		; display result
00023E  1  A5 23        		lda		DIVISR+1
000240  1  20 60 FE     		jsr		RDHEXTD		; and remainder
000243  1  4C 04 FF     		jmp		RESTART
000243  1