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

000000r 1               ;
000000r 1               ; ACORN System 1 Applications: Square Root
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               RESTART	:=		$FF04		; Monitor renentry point
000000r 1               RDHEXTD	:=		$FE60		; write double hex to display
000000r 1               QDATFET	:=		$FE88		; quad data fetch
000000r 1               ;
000000r 1               		.org			$0200
000200  1               ;
000200  1               SQL		:=		$20
000200  1               SQH		:=		$21
000200  1               ROOT	:=		$22
000200  1               SUBL	:=		$23
000200  1               SUBH	:=		$24
000200  1               ;
000200  1  F8           SQRDEC:	sed					; entry point for decimal square root
000201  1  F0 01        		beq		SQROOT		; always branch
000203  1  D8           SQRHEX:	cld					; entry point for hexadecimal square root
000204  1  84 21        SQROOT:	sty		SQH			; clear square to prompt
000206  1  84 20        		sty		SQL
000208  1  A2 20        		ldx		#SQL
00020A  1  20 88 FE     		jsr		QDATFET		; fetch the number whose root is to be found
00020D  1  84 24        		sty		SUBH		; clear high part of subtracting number
00020F  1  84 22        		sty		ROOT		; clear root
000211  1  C8           		iny
000212  1  84 23        		sty		SUBL		; subtract 001 at start
000214  1  A4 20        		ldy		SQL			; use Y & X as double sized accumulator
000216  1  A6 21        		ldx		SQH
000218  1  38           NXTSUB:	sec					; subtract SUB from X & Y
000219  1  98           		tya
00021A  1  E5 23        		sbc		SUBL
00021C  1  A8           		tay
00021D  1  8A           		txa
00021E  1  E5 24        		sbc		SUBH
000220  1  AA           		tax
000221  1  90 14        		bcc		RESULT		; if negative then stop
000223  1  A9 00        		lda		#$00		; not finished yet, increment root
000225  1  65 22        		adc		ROOT
000227  1  85 22        		sta		ROOT
000229  1  A5 23        		lda		SUBL		; increment SUB
00022B  1  69 02        		adc		#$02
00022D  1  85 23        		sta		SUBL
00022F  1  A5 24        		lda		SUBH
000231  1  69 00        		adc		#$00
000233  1  85 24        		sta		SUBH
000235  1  90 E1        		bcc		NXTSUB		; there can be no carry: branch always
000237  1  A5 22        RESULT:	lda		ROOT
000239  1  20 60 FE     		jsr		RDHEXTD		; display answer
00023C  1  4C 04 FF     		jmp		RESTART
00023C  1