# multiply  subroutine example for SPIM
	
	.data
msg:	.asciiz "The product is "
	
	.text		# this is program code
	.align 2	# instructions must be on word boundaries
	.globl main	# main is a global label
	
main:
	# multiply 128 * 256
	addi $a0,$zero,128	
	addi $a1,$zero,256
	jal multiply
	
	move $s0,$v0
	li $v0,4
	la $a0, msg
	syscall

	li $v0,1
	move $a0,$s0
	syscall
	
	li $v0,10
	syscall
	
	
# ---------------------------------
# mult subroutine needs some registers
# so we save $t0 first
	
multiply:	
	sub $sp,$sp,4	# make room for $t0
	sw  $t0,0($sp)  # put t0 on the stack

	# start with $t0 = 0
	add $t0,$zero,$zero
mult_loop:	
	# loop on a1
	beq $a1,$zero,mult_eol

	add $t0,$t0,$a0
	sub $a1,$a1,1
	j mult_loop

mult_eol:	
	# put the result in $v0
	add $v0,$t0,$zero

	# restore $t0
	lw $t0,0($sp)
	add $sp,$sp,4
	jr $ra