# Sum-soln.asm
#
# Author : Archana Chidanandan, 09/13/2004
#
# This program calculates the sum of the first N integers.
#
# This program demonstrates the use of procedures using the "jal" and "jr" instructions.
# It is Sum.asm modified to follow the MIPS register conventions.
#
# NOTE : THIS PROGRAM ADHERES TO THE MIPS REGSITERS CONVENTIONS.



	.text
	.globl main
      .globl SumCal
      .globl loop
      .globl exit

main:
	la	$t0, N		
	lw	$s0, 0($t0)	      # Load the value of N

      move  $a0, $s0		# Move the argument(N) to register $a0
	jal     SumCal		# Call method "SumCal"
      move 	$s3, $v0		# Move the return value to register $s3	

	la	$t0, SumOfN
	sw	$s3, 0($t0)	      # Store sum of first 
					# N integers to memory

	li	$v0, 10		# Prepare to Exit
	syscall			# End of program

#####################################################################
#
#   SumCal - Procedure that calculates the sum of first N integers.
#   input parameter - N 
#   return value - Sum
#
#####################################################################

SumCal:				# Procedure to calculate 
					# sum of first N integers
	li 	$t2, 0		# i = 0
	li	$t3, 0  	      # Sum = 0
loop:
	beq	$t2, $a0, exit    # if ( i == N ), quit
	addi	$t2, $t2, 1	      # i = i + 1
	add	$t3, $t3, $t2	# Sum = Sum + i
	j 	loop
exit:
	move  $v0, $t3
	jr	$ra		# Return to calling program


	.data
N:		.word  3
SumOfN :	.word  0