Sum of Integers
	MIPS Code Examples

#
# This program reads integers until -1 and reports their sum.
# 
        .text
        .globl  main
main:
        subu    $sp, $sp, 12            # Make room on the stack.
        sw      $ra, 0($sp)             # Save the return address.
        sw      $s0, 4($sp)             # Save $s0
        sw      $s1, 8($sp)             # Save $s1

        # Place a zero in the sum
        li      $s1, 0

        # Issume a prompt and read a string.
read:   
        li      $v0, 4                  # String
        la      $a0, prompt
        syscall
        li      $v0, 5                  # Read int, into $s0
        syscall
        move    $s0, $v0

        # See if it's a -1, and proceed to print if so
        li      $t0, -1
        beq     $s0, $t0, printtot

        # Add to total
        add     $s1, $s1, $s0

        # Round again
        j       read

printtot:
        # Print the total
        li      $v0, 4
        la      $a0, tmsg
        syscall
        li      $v0, 1
        move    $a0, $s1
        syscall
        li      $v0, 4
        la      $a0, nl
        syscall

        # Return
        lw      $s1, 8($sp)             # Restore $s1
        lw      $s0, 4($sp)             # Restore $s0
        lw      $ra, 0($sp)             # Restore the return address.
        addu    $sp, $sp, 12            # Pop the stack
        jr      $ra
# Note:  The order in which the registers are restored is not important.
# What matters is that each value is restored to the correct offset of
# from $sp.  That is, since we put $s0 at 4($sp) on the way in, we must
# restore it from 4($sp) on the way out.  Also be sure to adjust the the
# stack by the same amount and in the opposite direction when you return.

        .data
prompt: .asciiz ">"                     # Input prompt
tmsg:   .asciiz "The total is: "        # Total message.
nl:     .asciiz "\n"                    # Newline