0001 f800                    	org	$f800
0002                         
0003                         start
0004 f800 8e 00 ff           	lds	#$00ff
0005                         
0006 f803 cc 56 78           	ldad	#$5678		* least significant word
0007 f806 37                 	pshb
0008 f807 36                 	psha
0009 f808 cc 12 34           	ldad	#$1234		* most significant word
0010 f80b 37                 	pshb
0011 f80c 36                 	psha
0012                         
0013 f80d cc de f0           	ldad	#$def0		* least significant word
0014 f810 37                 	pshb
0015 f811 36                 	psha
0016 f812 cc 9a bc           	ldad	#$9abc		* and most
0017 f815 37                 	pshb
0018 f816 36                 	psha
0019                         
0020 f817 bd f8 24           	jsr	add32		* do the add
0021 f81a 32                 	pula			* uncover the result
0022 f81b 32                 	pula
0023 f81c 32                 	pula
0024 f81d 32                 	pula
0025                         
0026 f81e 32                 	pula			* then get the result into regs
0027 f81f 33                 	pulb			* 12345678 +
0028 f820 38                 	pulx			* 9abcdef0 =
0029                         *				  acf13568
0030                         
0031                         
0032 f821 7e f8 21           loop	jmp	loop
0033                         
0034                         
0035                         * add two 32 bit quantities which were passed on the stack.
0036                         * the additions are done one byte at the time and the first
0037                         * argument is overwritten with the result.
0038                         
0039                         * on entry, the stack looks like this:
0040                         
0041                         *    a[0]			<---  sp+10  <--- x+9
0042                         *    a[1]			<---  sp+9
0043                         *    a[2]			<---  sp+8
0044                         *    a[3]			<---  sp+7
0045                         *    b[0]			<---  sp+6
0046                         *    b[1]			<---  sp+5
0047                         *    b[2]			<---  sp+4
0048                         *    b[3]			<---  sp+3
0049                         *    return_address_low		<---  sp+2
0050                         *    return_address_high	<---  sp+1  <--- x
0051                         *				<---  sp
0052                         
0053                         * just before exit, it looks like this:
0054                         *    a[0]+b[0]			<---  sp+10
0055                         *    a[1]+b[1]			<---  sp+9
0056                         *    a[2]+b[2]			<---  sp+8
0057                         *    a[3]+b[3]			<---  sp+7
0058                         *    b[0]			<---  sp+6
0059                         *    b[1]			<---  sp+5
0060                         *    b[2]			<---  sp+4
0061                         *    b[3]			<---  sp+3
0062                         *    return_address_low		<---  sp+2
0063                         *    return_address_high	<---  sp+1   <--- x
0064                         *				<---  sp
0065                         add32:
0066 f824 ce 00 00           	ldx	#0
0067 f827 30                 	tsx
0068 f828 18 ce 00 04        	ldy	#4
0069 f82c 0c                 	clc
0070                         addloop:
0071 f82d a6 09              	lda	9,x
0072 f82f a9 05              	adca	5,x
0073 f831 a7 09              	sta	9,x
0074 f833 09                 	dex
0075 f834 18 09              	dey
0076 f836 26 f5              	bne	addloop
0077                         
0078 f838 39                 	rts
0079                         
0080 fffe                    	org	$fffe
0081 fffe f8 00              	fdb	start