8051 Program - unsigned 16bit division

; subroutine UDIV16

; 16-Bit / 16-Bit to 16-Bit Quotient & Remainder Unsigned Divide

;

; input: r1, r0 = Dividend X

; r3, r2 = Divisor Y

;

; output: r1, r0 = quotient Q of division Q = X / Y

; r3, r2 = remainder

;

; alters: acc, B, dpl, dph, r4, r5, r6, r7, flags

UDIV16:	mov r7, #0	;clear partial remainder
	mov r6, #0
	mov B, #16	;set loop count
div_loop:	clr C	;clear carry flag
	mov a, r0	;shift the highest bit of
	rlc a	;the dividend into...
	mov r0, a
	mov a, r1
	rlc a
	mov r1, a
	mov a, r6	;... the lowest bit of the
	rlc a	;partial remainder
	mov r6, a
	mov a, r7
	rlc a
	mov r7, a
	mov a, r6	;trial subtract divisor
	clr C	;from partial remainder
	subb a, r2
	mov dpl, a
	mov a, r7
	subb a, r3
	mov dph, a
	cpl C	;complement external borrow
	jnc div_1	;update partial remainder if
		;borrow
	mov r7, dph	;update partial remainder
	mov r6, dpl
div_1:	mov a, r4	;shift result bit into partial
	rlc a	;quotient
	mov r4, a
	mov a, r5
	rlc a
	mov r5, a
	djnz B, div_loop
	mov a, r5	;put quotient in r0, and r1
	mov r1, a
	mov a, r4
	mov r0, a
	mov a, r7	;get remainder, saved before the
	mov r3, a	;last subtraction
	mov a, r6
	mov r2, a
	ret

Source: Maths Subroutines for the 8051 microcontroller, W.G.Marshall 2002

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Related topics:
8051 Program - signed 8bit division   |   8051 Program - unsigned 8bit division   |   8051 Program - signed 16bit division   |   8051 Program - signed 32bit division   |   8051 Program - unsigned 32bit division   |   8051 Program - memory subroutines   |   8051 Program - math subroutines   |   8051 Program - conversion subroutines

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