I don't know how to chech if a string is symmetric or not in mips

Question

i'am new at StackOverFlow, i get into trouble and i need your help. I'am student and i need to write a MIPS program that checks if one string is symmteric. *sample symmetric strings : ana, asddsa, fillif and so on.

This is my first line of code where i am reading string into an array, but i stucked at the symmetric part.

.data

array: .space 50 # char a[50];
.text

readText:

    li $v0,8 # input
    la $a0,array # loadiraj memorija vo adresata
    li $a1,20 #obezbedi memorija za string
    move $t0,$a0 #zachuvaj string vo $t0
    syscall

symmetry:

Please give me an opinion, how i should start with symmetry part. Thanks

Can you do it in C? If not, then you need help with an algorithm. If so, then tell us what C construct you're struggling to translate into MIPS. — Erik Eidt, Apr 12 '20 at 19:23
I have problem at this line `if(string1[i] != string1[length-i-1]){` i don't know how to get i-element of an array then to check if they are same or not. Thanks — Filip Gorgievski, Apr 12 '20 at 21:45

score 0 · Accepted Answer · answered Apr 12 '20 at 23:00

Array references are done with pointer arithmetic. First we have to know the location of the variables string1 and i. Let's assume string1 is in $a0 and i is in $t0. We will need to add these two variables together. Whenever we do an arithmetic operation we have to send the result somewhere, and here the idea is to a send the result to a new as-yet-unused register, say $t1. ($a0 and $t0 in this scenario would be a bad place to send the result since those registers hold values we'll need later on in the current or next iteration of the loop.)

add $t1, $a0, $t0

Next dereference that temporary pointer using lbu:

lbu $t2, 0($t1)

again targeting an otherwise unused register.

The C version using three address code would look like this:

char *p;
char ch;

p = string1 + i;
char ch = *p;

Comparison is done with either the beq or bne instruction, both of which take two registers to compare (for equality or inequality, respectively) and a branch target in the form of a label.

We use conditional branches to skip ahead for if-then. The idea is to reason when to skip the then part — and when to skip is the opposite of the if condition as we would write it in C. In assembly: skip this if that, whereas in C: do this if that. Thus, the opposite condition is tested in assembly in order to skip around the then-part.

Thank you a lot sir. – Filip Gorgievski Apr 12 '20 at 23:36 — Filip Gorgievski, Apr 12 '20 at 23:36

I don't know how to chech if a string is symmetric or not in mips

1 Answers1