; UFRGS - INF - Bruno Mascali - 2024
; Check if the number (1 <= number <= 129) at address 80h is prime
; A prime number is a natural number that is divisible only by 1 and itself

; ----- DATA
        	org    h80
number:  	DB 2	; The number to check for primality
test_divisor: 	DB 0    ; Current divisor being tested
output:  	DAB [9] ; Output message buffer
outputend:	DB 0	; buffer end
msgsize: 	equ outputend-output

; ----- ERASE MESSAGE -----
; RA = 0
; RB = counter
; RX = position

        org    0
	LDR 	A #0		; will write 0's at output
	LDR 	B #msgsize	; msg buffer size
	LDR 	X #output	; buffer address
apaga:	STR 	A 0,X		; erase this position
	ADD 	X #1		; advance
	SUB	B #1		; one less to go
	JZ	start_up	; if done, start the algorithm
	JMP	apaga		; goto erase next

; ----- BEGIN MAIN CODE -----
; RA = number
; RB = current divisor
	
start_up:    
        LDR    A, number
        SUB    A, #1
        JZ     not_prime    ; If number is 1, it is not prime

        LDR    A, #0
        ADD    A, #1
        STR    A, test_divisor    ; Initialize test_divisor to 1
        LDR    B, test_divisor    

outer_loop:    
        ADD    B, #1        
        STR    B, test_divisor
        LDR    A, number
    
division: 
        SUB    A, test_divisor    
        JZ     check_if_prime    ; If the result is zero, a factor is found
        JN     outer_loop        ; If not zero and not negative, continue with next divisor
        JMP    division          ; Continue the division process

check_if_prime:
        LDR    A, number
        STR    B, test_divisor
        SUB    A, test_divisor        
        JZ     prime             ; If number == test_divisor, it is prime
        JMP    not_prime         ; Otherwise, it is not prime

prime:    
        LDR    A, #'P'
        STR    A, output
        LDR    A, #'r'
        STR    A, output+1
        LDR    A, #'i'
        STR    A, output+2
        LDR    A, #'m'
        STR    A, output+3
        LDR    A, #'e'
        STR    A, output+4
        HLT                     ; Halt after writing "prime"

not_prime:        
        LDR    A, #'C'
        STR    A, output
        LDR    A, #'o'
        STR    A, output+1
        LDR    A, #'m'
        STR    A, output+2
        LDR    A, #'p'
        STR    A, output+3
        LDR    A, #'o'
        STR    A, output+4
        LDR    A, #'s'
        STR    A, output+5
        LDR    A, #'i'
        STR    A, output+6
        LDR    A, #'t'
        STR    A, output+7
        LDR    A, #'e'
        STR    A, output+8
        HLT                     ; Halt after writing "composite"
        
; ----- END OF FILE -----