How to pop from the stack in MIPS assembly?

Question

I'm trying to learn MIPS assembly, since I've got some free time, and I'm trying to write a program that pushes numbers on to a stack, then pops them off. I want it to count the number of numbers popped before reaching a negative number and then each time it gets a negative one keep count of how many negative and positive numbers were popped.

so far I got this:

 #count the number of negative words on the stock by poping the stack until a non-    negative word is found 
#and print out the number of words found

.text
.globl main
#this code reads the numbers from the data area and stores in them in a stack
#the numbers are located in the test area and the number of numbers in the num area

main:   la $t0, test
lw $t1, num
loop:   lw $t2,($t0)
sub $sp, $sp, 4
sw $t2($sp)
add $t0, $t0, 4
add $t1, $t1, -1
bnez $t1, loop


#pop from the stack and print the number of numbers in the stack before a nonnegative number is reached 
#then keep count of how many negative and positive ones there are total

#code I cannot come up with would go here

.data
test:   .word
2, 0xfffabfff,2,-4,-9,0x99999999,0x90000000,-2147479536,0x80000000
num:    .word 10
ans:    .asciiz "Number is = "
endl:   .asciiz "\n"

I got it to push right, far as I can tell, but I cannot figure out the pushing and counting right. what do I have to do from here?

Solution

A pop would be the opposite of a push. So if you use this to push $t2:

sub $sp,$sp,4
sw $t2,($sp)

You would pop it with:

lw $t2,($sp)
addiu $sp,$sp,4

Counting the number of negative words on the stack would be a matter of having a loop which pops a word off the stack, uses BGEZ to exit the loop if the popped value is >=0 or otherwise increases a counter and repeats.

Comments

[Stefano Sanfilippo]

Extreme nitpicking, I know, but sub with immediate does not exist, it should be addi $sp, $sp, -4.

[Michael]

It's most likely recognized as a pseudo-instruction by the assembler and translated into addiu.