; Written by: Deepak Kumar. March 25, 2024
; File: divSubroutine.asm
; Program to divide two numbers by repeated subtraction to get quotient and remainder
; Algorithm
;   A = 22
;   B = 7
;   quotient = 0
;   while A >= B do
;       A = A - B
;       q = q + 1
;   remainder = A
        .ORIG       x6000
A       .FILL       22
B       .FILL       7
        .END
;        
; The main program
;
        .ORIG       x600A
START   LD      R2, A
        LD      R3, B
        JSR     DIVMOD
        HALT
; DIVMOD
; R2 contains dividend (A), R3 contains divisor (B)
; Result is put in R0 (Quotient) and R1 (remainder)
; R4 is used to store -R3
; R5 is used to store the result of subtraction (A - B)
; Registers: R0 and R1 will return results.
;
DIVMOD  ADD     R1, R2, #0  ; R1 = R2 (A)
        NOT     R4, R3      ; R4 = -R3: R4 = NOT(R3) and  Adding 1 to R4
        ADD     R4, R4, #1  
        AND     R0, R0, #0  ; R0 = 0
; while R1 >= R3 : R5 = R1 - R3 : R5 = R1 + R4
LOOP    ADD     R5, R1, R4
        BRn     DONE
; do
        ADD     R1, R1, R4  ; R1 = R1 - R3
        ADD     R0, R0, #1  ; R0 = R0 + 1  
        BR      LOOP
DONE    RET
        .END