# This program takes two arguments, both required to be
# decimal or hexadecimal integers, and returns their sum.

        .data
plus:
        .asciiz " + "
equals:
        .asciiz " = "
newline:
        .asciiz "\n"
space_character:
        .asciiz " "
usageMessage:
        .asciiz "\nUsage: <first number> <second number>\n"

        .text
main:
        subu    $sp,32          # create stack frame
        sw      $ra,28($sp)     # save return address
        sw      $s2,24($sp)     # save $s2 (y)
        sw      $s1,20($sp)     # save $s1 (x)
        sw      $s0,16($sp)     # save $s0

        move    $s0,$a1         # $s0 = argv

        bne     $a0,2,usageError # must have exactly two arguments (both integers)

        # decode x

        lw      $a0,0($s0)      # $a0 = address(1st argument string) = argv[0]
        jal     decode_int
        move    $s1,$v0         # store the result ($v0) in x ($s1)

        # decode y

        lw      $a0,4($s0)      # $a0 = address(2nd argument string) = argv[1]
        jal     decode_int
        move    $s2,$v0         # store the result ($v0) in y ($s2)

        # print x + y = z

        move    $a0,$s1         # x
        li      $v0,1           # print_int
        syscall                 #

        la      $a0,plus        # +
        li      $v0,4           # print_string
        syscall                 #

        move    $a0,$s2         # y
        li      $v0,1           # print_int
        syscall                 #

        la      $a0,equals      # =
        li      $v0,4           # print_string
        syscall                 #

        add     $a0,$s1,$s2     # z
        li      $v0,1           # print_int
        syscall                 #

        la      $a0,newline     # \n
        li      $v0,4           # print_string
        syscall                 #

all_done:
        lw      $ra,28($sp)     #
        lw      $s2,24($sp)     #
        lw      $s1,20($sp)     #
        lw      $s0,16($sp)     #
        addu    $sp,$sp,32      #
        j       $ra             #

        # Print the usage error message

usageError:
        la      $a0,usageMessage # usage error
        li      $v0,4            # print_str
        syscall                  #
        j       all_done         #

# Converts an integer value from a textual representation to its machine representation
# Requires:
#     a0   the address of the start of the textual representation
#          Must be a null terminated string.
# Returns:
#     v0   the machine representation of the integer value
#          -1 => decode error

# Project 1: Implement this procedure
decode_int:
        move    $v0,$zero        # cumulative decoded value = 0
        jr    $ra                # return