mul2x2.asm

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;
; R4R5R6R7 = R6R7 * R2R3
;
; use Acc,B,R1..R7
;

.global	mul2x2

mul2x2:	mov	a,r3
	mov	b,r6
	mul	ab	;R3R6
	xch	a,r6	;A=R6 R6=lowR3R6
	mov	r1,b	;R1=highR3R6
	mov	b,r2
	mul	ab	;R2R6
	mov	r5,a	;R5=lowR2R6
	mov	r4,b	;R4=highR2R6
	mov	a,r3
	mov	b,r7
	mul	ab	;R3R7
	xch	a,r7	;R7=lowR3R7
	xch	a,b	;B=7 A=highR3R7
	add	a,r6
	xch	a,r5	;R5=lowR3R6+highR3R7
	addc	a,r1
	mov	r6,a	;R6=Carry(lowR3R6+highR3R7)+lowR2R6+highR3R6
	mov	a,r2
	mul	ab	;R2R7
	add	a,r5
	xch	a,r6	;R6=lowR2R7+lowR3R6+highR3R7
	addc	a,b
	mov	r5,a	;R5=Carry(lowR2R7+lowR3R6+highR3R7)
	clr	a	; +highR2R7+Carry(lowR3R6+highR3R7)+lowR2R6+highR3R6
	addc	a,r4
	mov	r4,a	;R4=highR2R6+Carry(Carry(lowR2R7+lowR3R6+highR3R7)
	ret		; +highR2R7+Carry(lowR3R6+highR3R7)+lowR2R6+highR3R6)