## ECE2030 Intro to Computer Engineering
##
## Prime identifier
## 
## Author: Prof. Hsien-Hsin S. Lee			
## 
## School of Electrical & Computer Engineering
## Georgia Institute of Technology
## Atlanta, GA 30332
##
## leehs@gatech.edu
##
##							 
		
	.rdata
        .globl string
string:	
	.ascii " is a prime number\n"	
	.word 0x00000000
LB:	
	.ascii "Lower Bound?"
	.word 0x00000000
UB:	
	.ascii "Upper Bound?"
	.word 0x00000000		

# Standard startup code.  Invoke the routine main with no arguments.

	.text
	.globl __start
__start: jal main
	addu $0, $0, $0		# Nop
	addiu $v0, $0, 10
	syscall			# syscall 10 (exit)


	.globl main
main:
	addu $20, $0, $31	# Save return PC


	# set up initial values
	li $v0, 4
	la $a0, LB
	syscall
	li $v0, 5
	syscall
	addu   $12, $0, $v0             # Enter Lower Bound in $12

	li $v0, 4
	la $a0, UB
	syscall
	li $v0, 5
	syscall
	addu   $20, $0, $v0		# Enter Upper Bound in $20
	
	addiu  $13, $0, 1		# Load immediate value into r3
	add    $16, $0, $0		# clear $16 before entering the loop
					# If $16=2, a prime number is detected
Loop:		
			
	divu  $12, $13			# $12 / $13	
	mfhi  $15			# Get remainder from HI
	bne   $15, $0, Rem_notzero
	addiu $16, $16, 1		# # of occurences when remainder = 0 
	beq   $13, $12, Next		# The factor is itself if condition is true
					
Rem_notzero:
	addiu $13, $13, 1		# $13 = $13 + 1
	j     Loop			# 
	
Next:
	beq   $16, 2, Print_prime       # check prime number
Cont:
	add   $16, $0, $0		# clear $16
	addiu $12, $12, 1		# Increment the number under test
	bgt   $12, $20, Exit		# exit if upper bound reached 
	addiu $13, $0, 1		# clear $13 = 1
	j     Loop

        .globl Print_prime
Print_prime:
	li $v0, 1 # syscall to print number
	add $a0, $12, $0
	syscall
	li $v0, 4 # syscall to print string
	la $a0, string
	syscall 
	j  Cont	

Exit:	
	jr $31