## Q5.ASM
## AUTHOR:
## STUDENT ID:
## ABOUT: Application finds max of 10 values
##        Using the MAX3 function


## Variable Mapping:
#   $t7, base address for T20Numbers
#   $t6, max index
#   $t5, current index
#   $t4, unused
#   $t3, unused
#   $t2, Value of Max loaded from address.
#   $t1, Address to Max
#   $t0, address of word to extract

.data

T20Numbers:     .word  12,20,-9,13,15,18,-8,10,20,-14   # The 10 numbers
Max:            .space 4

.macro getnum(%ax)
sll $t0, $t5, 2                                         # multiply our index by 4 to get word offset
add $t0, $t7, $t0                                       # add to get word address.
lw %ax, 0($t0)                                          # load word into ax (a0,a1,a2)
.end_macro

.text

la $t7, T20Numbers                                      # get address of first element of T20Numbers
li $t6, 9                                               # maximum address for our word list.
li $t5, 0                                               # track which element we're starting on.

## MAIN PROGRAM LOOP ##############################################################################
getmax:         getnum($a0)                             # populate $a0 with number from T20Numbers.
                addi $t5, $t5, 1                        # add 1 to our index.
                getnum($a1)                             # populate $a1 with number from T20Numbers.
                addi $t5, $t5, 1                        # add 1 to our index.
                getnum($a2)                             # populate $a2 with number from T20Numbers.

                jal max3                                # check max between these three numbers
                jal checkmax                            # set the max value if need be.

                beq $t5, $t6, exit                      # exit procedure if finished.

                                                        # note: this is dumb, but it works.
                addi $t5, $t5, -1                       # otherwise decrement by 1 and repeat
                                                        # end note

                j getmax                                # jump to label for repeat
## END MAIN PROGRAM LOOP ##########################################################################

## CHECK MAX SUBROUTINE ###########################################################################
checkmax:       la $t1, Max                             # load address of max into $t1
                lw $t2, 0($t1)                          # load content of max into $t2
                bge $v0, $t2, setmax                    # check if new max > old max if so set.
                jr $ra                                  # otherwise just return
setmax:         sw $v0, 0($t1)                          # store $v0 as new max
                jr $ra
## END CHECK MAX SUBROUTINE #######################################################################

## MAX SUB ROUTINE ################################################################################
max3:           add $v0, $a0, $zero         # copy $a0 to $v0
                sub $t0, $a1, $v0           # if $a1 < $v0 then $t0 is negative
                bltz    $t0, good           # if $t0 is < 0 nothing changes
                add     $v0, $a1, $zero     # otherwise $a1 is highest
good:           sub $t0, $a2, $v0           # if $a2 < $v0 then $t0 is negative
                bltz    $t0, done           # if $t0 is < 0 nothing changes
                add $v0, $a2, $zero         # $a2 becomes highest
done:           jr $ra                      # return to caller
## END MAX SUB ROUTINE ############################################################################

## EXIT HANDLING ##################################################################################
exit:           lw $a0, 0($t1)          # load the max value into $a0
                addi $v0, $zero, 1      # request system call function 1 output
                syscall                 # issue systemcall.
## END EXIT HANDLING ##############################################################################