; Div8_8

; Version 1.0
; Date: November 11, 2014
; Written By : Yoseph Yegezu
; From text book 'The AVR Microcontroller and Embedded systems'Chapter 5 Page 167

.INCLUDE <m328pdef.inc>

			
.CSEG

.DEF Num=R20
.DEF Denominator=R21
.DEF Quotient=R22

.ORG 0x0000

	ldi Num, 0xAA		  
	ldi Denominator, 0x55	  
	//call the 8 bit division
    rcall Div8
    ret	
/************************************
 * subroutine divides unside 8bit by 8bit
 * Quotient = Numerator/Denominator *
 *     r22  =     r20 / r21  
 * with remainder in r20            *
 ************************************/

Div8: 
    clr  Quotient          // r22

// quotient is going to increment by 1 everytime L1 loops
// loop  L1 stops when the numerator-denominator = less than the demoninator

L1:
	inc Quotient
	
	sub  Num,Denominator  // r20,r21
	brcc L1

//since the quotient is incremented by 1 when the loop began, after the loop quotient is dec
	dec  Quotient

//notice L1 is going to branch off when the numerator is no lnger divisiable by the denominator 
//which means L1 is branching off when numerator-denominator results in a negative value.
//therefore, the denominator is going to be added to the numerator after the loop.
	add  Num,Denominator  // r20,r21
	
	ret