org	$f800

start
	lds	#$00ff

	ldad	#$5678		* least significant word
	pshb
	psha
	ldad	#$1234		* most significant word
	pshb
	psha

	ldad	#$def0		* least significant word
	pshb
	psha
	ldad	#$9abc		* and most
	pshb
	psha

	jsr	add32		* do the add
	pula			* uncover the result
	pula
	pula
	pula

	pula			* then get the result into regs
	pulb			* 12345678 +
	pulx			* 9abcdef0 =
*				  acf13568


loop	jmp	loop


* add two 32 bit quantities which were passed on the stack.
* the additions are done one byte at the time and the first
* argument is overwritten with the result.

* on entry, the stack looks like this:

*    a[0]			<---  sp+10  <--- x+9
*    a[1]			<---  sp+9
*    a[2]			<---  sp+8
*    a[3]			<---  sp+7
*    b[0]			<---  sp+6
*    b[1]			<---  sp+5
*    b[2]			<---  sp+4
*    b[3]			<---  sp+3
*    return_address_low		<---  sp+2
*    return_address_high	<---  sp+1  <--- x
*				<---  sp

* just before exit, it looks like this:
*    a[0]+b[0]			<---  sp+10
*    a[1]+b[1]			<---  sp+9
*    a[2]+b[2]			<---  sp+8
*    a[3]+b[3]			<---  sp+7
*    b[0]			<---  sp+6
*    b[1]			<---  sp+5
*    b[2]			<---  sp+4
*    b[3]			<---  sp+3
*    return_address_low		<---  sp+2
*    return_address_high	<---  sp+1   <--- x
*				<---  sp
add32:
	ldx	#0
	tsx
	ldy	#4
	clc
addloop:
	lda	9,x
	adca	5,x
	sta	9,x
	dex
	dey
	bne	addloop

	rts

	org	$fffe
	fdb	start