Printing prime numbers in MIPS
 

I need to get a MIPS program to print out the first 30 prime numbers and to compute the first 200 (strange, but its the assignment). I can figure out what's wrong with this program. All it does is print 2's out in an infinite loop and I cannot figure out why. We're only supposed to use three procedures (main, testprime, and print) but I'm so bad that I decided to use more. Thank you in advance for helping me.

   .text

   .globl main



main:

        # intialize values

        ori $s0, $0, 20

        ori $s1, $0, 30

        ori $s2, $0, 2

        ori $s3, $0, 2



loop:

        ori $s3, $0, 2        

        beq $s0, $0, exit

        beq $t0, $s4, print

        j testprime



testprime:

        beq $s2, $s3, prime

        div $s2, $s3

        mfhi $t1

        beq $t1, $0, noprime

        addi $s3, $s3, 1

        j testprime



noprime:

        ori $t0, $0, 0

        addi $s2, $s2, 1

        j loop





prime:

        ori $t0, $0, 1

        sub $s0, $s0, $s4

        addi $s2, $s2, 1

        j loop        

        



print:

        ori $t0, $0, 0

        beq $s1, $0, loop

        sub $s1, $s1, $s4

        li $v0, 1

        or $a0, $0, $s2

        syscall

        li $v0, 4

        la $a0, newline

        syscall

        j loop

        



exit:

        li $v0, 10

        syscall



.data

newline: .asciiz "\n"

Re: Printing prime numbers in MIPS
 

Hmm. Sorry I dont know mips assembly but on line 12

ori $s3, $0, 2

It looks like your resetting something back to 2. Just an educated guess.;) Good luck!

Re: Printing prime numbers in MIPS
 

Actually it was something stupid, I never initialized $s4 to 1 so the loop never exited. Got the answer from elsewhere, but now my problem is that my output is non-prime numbers which is the opposite of what I want.

Re: Printing prime numbers in MIPS
 

Hmm.. Switch prime and noprime maybe :)

Re: Printing prime numbers in MIPS
 

If only the world were that sweet.

Re: Printing prime numbers in MIPS
 

So why aren't you using an empty block of stack and filling it with primes so then you only need to divide by earlier resolved primes instead of the entire set of numbers?

My mind is a bit tired, but as a rule you should always heavily comment your code. Right now would be a good time to do so. Have you tried single stepping your code yet?

Re: Printing prime numbers in MIPS
 

By the way. You don't seem to initialze the temporary register $t0.

(See loop:)

gotta run, will check back when I get back!

Re: Printing prime numbers in MIPS
 

$t0 and $s4 aren't initialized!
Not sure what you're using $s0 for.
You change the register containing the found prime before printing it. Should copy it into $s4 as you use that as part of your print test.
Not really sure what your logic on prime: is actually doing.

Re: Printing prime numbers in MIPS
 

Well I already noted $s4 wasn't initialized. You're right about commenting my code I usually do but I was just tired. I didn't notice about $t0 though.

My logic was sort of checking each number (n) against a counter which started out as 2 then incremented. If n mod counter equaled zero then I jumped out and didn't count it as prime, but somehow I messed up.

I figured out that I was incrementing my answer before the display so that's what was wrong. I even managed to backtrack to fulfill the original condition of my assignment.