input.txt

.data
str: .asciiz "aba"
n: .word 0

.text

la x5 str	
la x6 n
sub x7 x6 x5
addi x6 x6 -2	
addi x7 x7 -1	
srli x7 x7 1	
addi x8 x0 1	

loop:
	beq x7 x0 exit
    lb x10 0(x5)
    lb x11 0(x6)
    beq x10 x11 else
    	add x8 x0 x0
    	jal x0 exit
    else:
    addi x5 x5 1
    addi x6 x6 -1
    addi x7 x7 -1
    jal x0 loop
exit: