Compute parity of a number

parity.asm

#Hunter Scott
#Version for MARS
#declare and reserve space for data and variables after .data
.data
#string constant
title: .asciiz "Program computes the pariety of number"
prompt: .asciiz "Input a number please: "
o_title: .asciiz "The pariety is "
# newline junk
newline: .byte 10,13,00,00
#force address back to word boundry
.align 2
#integer variables
n: .word 0
pariety: .word 0
#instructions come after .text directive
.text

main:
#print everything out
#puts title
li $v0, 4
la $a0, title
syscall
#print out carriage return and  line feed
#putc '\n'
li $v0, 4
la $a0, newline
syscall
#print out carriage return and line feed
#putc '\n'
li $v0, 4
la $a0, newline
syscall
#prompt for user input
#puts prompt
li $v0, 4
la $a0, prompt
syscall
#read an integer, N
#geti $a0
li $v0, 5
syscall
add $a0, $v0, $zero #now the number read in is in $a0
#
###### Real program logic starts here #######
#
#

#prepare for subroutine
addi $sp, $sp, -16 #allocate space on stack
sw $ra, 4($sp) #push ra on stack
sw $a0, 0($sp) #push number to test on stack
jal PARIETY
#print carriage return and line feed
#putc '\n'
li $v0, 4
la $a0, newline
syscall
#print out output title screen
#puts o_title
li $v0, 4
la $a0, o_title
syscall
#load result
lw $a0, 12($sp)
#print out result
#puti $a0
li $v0, 1
syscall
#print out carriage return and line feed
#putc '\n'
li $v0, 4
la $a0, newline
syscall
#end program and return to simulator
#done
li $v0, 10
syscall
###END OF PROGRAM###


PARIETY: 
#sw $ra, 8($sp) #push new $ra on stack
lw $v0, 0($sp) #load n
addi $t0, $0, 32 #reference
addi $t1, $0, 1 #reference for AND
add $t2, $0, $0 #initialize number of 1s count to 0
LOOP: beq $t0, $0, DONE #see if we have checked all 32 bits
and $t3, $v0, $t1 #AND together 1 and input
srl $v0, $v0, 1 #shift right
addi $t0, $t0, -1 #decrement iteration counter
bne $t3, $t1, LOOP #if the result is not a 1, loop 
addi $t2, $t2, 1 #increase numbers of ones found counter
j LOOP #then loop back 
DONE: and $t3, $t2, $t1 #once we've iterated through all 32 bits, bitmask the number of 1s counter with an AND to isolate last bit
add $a1, $0, $0 #assume result is even, if it's not, it'll get changed below.
sgt $a1, $t3, $0 #if the last bit was greater than 0, input was odd, so flag is 1
sw $a1, 12($sp) #store flag result
#lw $ra, 8($sp) #pop $ra from stack
jr $ra #return back to caller